NerveGear
The NerveGear is a helmet with a smooth, deep blue color. At the back, it has a wire of the same color stretched out of a long pad. It also has a battery and internal memory to store data from the games. Half of the NerveGear's weight is from its internal battery. The NerveGear's high density microwave transceivers can determine what the user's face looks like. The transceivers not only block every transmission from the brain to the body, but also from the body to the brain; while using it, the player is completely insensate to the physical world. To use the NerveGear, the player wears the game console over the head. Then, it's recommended that the player find a comfortable position to station the body, commonly being a bed. Afterwards, the game will load by the initiation words «Link Start».

Beater
Beater is derogatory term used by the players of Sword Art Online. It is meant to be an insult for beta-testers who play unfairly. Beaters are often discriminated and were often treated as unfair players who only care about themselves.

Clearer
a Clearer is an elite player who is higher level than most other players and focuses on leveling up, and getting better equipment in order to clear all levels of the game. Clearers are looked up to and admired by many with high regard due to their ability to fight on the front lines, which are the most dangerous parts of the game.

Guild
A Guild is a group of players, most on par with each other in regarding to levels, with an organized structure and a leader in various major online games.

*Guilds have unique features that allow players to interact differently from regular player to player interactions and guilds also offer several benefits to its members:

*Guild members have access to a common guild storage, which can be used to easily share items, such as potions, among themselves.

*The guild member list can be used for tracking the position of a fellow guild member, if the said member is not within a dungeon.

*Guild members are able to send short messages to one another. Does not work within a dungeon.

*Guilds have customizable emblems which appear on the guild members' top left interface, next to the player's HP bar, as well as next to the player's HP bar from another player's point of view.

*When guild members are in the same party, the players receive a slight increase in their stats.

*The only known drawback of being a member of a guild is that guild members are taxed whenever they earn money and the taxed money is sent to the guild's vault.

Player Killing
Player Killing (abbreviated as PK), is the act of killing another player in an online game.

Boss
A Boss, in video game terminology, is a unique computer-controlled monster or character that is much more powerful than an average monster or non-player character encountered in the game until that point and usually serves as a challenge to the player at the end of particular section of a game, usually a level or stage, or guarding a specific objective.

VRMMORPG
A VRMMORPG (short for Virtual Reality Massively Multiplayer Online Roleplaying Game) game is a multiplayer video game capable of supporting hundreds or thousands of players simultaneously. By necessity, they are played mostly on the Internet, and usually feature at least one persistent world. VRMMORPG's are most commonly played in the first person point of view, and are often very social as well as being serious much like other MMO's.

Artificial Intelligence
Artificial Intelligence (or A.I.), in the field of gaming and computer science, refers to the intelligence of the machines and the effort to re-create human-like intelligence in Non-Playable Characters (NPCs). In Sword Art Online, the system is generally known for having a mixture of NPCs with very advanced A.I. and NPCs with very poor A.I.

Solo Player
Solo Players are those who play alone and don't form any lasting parties with other players in Sword Art Online. Benefits include higher experience and undivided loot, but drawbacks include more danger to the individual if attacked with ailments like paralysis or by overwhelming odds. The people who comprised this type in SAO were generally beta-testers, since they were discriminated against by regular players who think that they only care about themselves.

Dungeon
A Dungeon is any type of adventuring location in an MMO, which is designed like a labyrinth or maze-like structure that has numerous paths, monsters, and rooms (for closed dungeons). Two main types of dungeons exist in Sword Art Online, Labyrinths and sub-dungeons.

Color Cursor
The Color Cursor in Sword Art Online and ALfheim Online is part of the visual display of a player. It appears over the heads of players, NPCs and monsters whenever the player focuses his or her gaze on the said players or NPCs, or if the said monsters are within the player's detection range, which can be increased by leveling the «Searching» skill. The cursor shows the threat of level of an entity towards the player.

Color Cursors do not appear inside of a building, as, for example, in restaurants it would be impossible to eat if the cursor kept appearing whenever a player focuses his or her gaze on another person.

Green
Players that have not directly committed an infraction receive a green cursor. Most players in Sword Art Online have green cursors. NPCs in Sword Art Online also have green cursors and also have an «NPC» tag under the HP bar.
Dangerous characters can still have green cursors by getting around the system. Monster PKing (player killing) or Sleep PKing will not turn a player's cursor from green to orange. Attacking an enemy in a safe zone deals no damage and will not change cursor color.

Defending against an attacking player or protecting a player who is being attacked by another player in a non-safe area will not change the player's color cursor. Total Loss Mode Duels will also not change a player's color cursor.

Orange
In Sword Art Online, players that have committed an infraction receive an orange cursor. An infraction is initiated typically by the first act of attacking a green player outside the safe zone.
An orange color cursor will gradually restore itself to a green color cursor within several hours for the first three infractions committed. For the fourth infraction, the orange color cannot be removed unless the player performs a quest. After the fifth infraction, a player's color cursor will remain permanently orange.

Players with orange cursors are unable to enter villages or streets that have the AREA effect on. If they try to get in these areas, they will be attacked by NPC guards until they leave the affected area. In order for an orange player to move around floors, they must either walk from floor to floor or use teleportation crystals.

Player Killers are granted permanent orange colors. While in the linguistic these players are referred to as "Red" players due to their interference with clearing the game, their cursors are not actually red.

Red
All active monsters have a red cursor of various shades. The shade of red can be used as a reference to the monster's power when compared to the player's level. The cursor of monsters that need to be killed for a quest appear with a narrow yellow border surrounding the cursor.

Col (Game Currency)
Col is the form of currency in the world of Sword Art Online. When players sell items to NPCs, the Col is listed under the market price, so as to not produce inflation. The valued currency of Sword Art Online is gathered swiftly from boss battles, as they yield a large amount of valuable loot, but the loot is usually shared among all participants of the boss battle. Other methods of acquiring col include killing monsters in dungeons or open fields, selling fruit that drop from trees (not a very efficient method, but it is favored by those who refuse to battle monsters), trading, Monster PK, and for orange guilds and players, ambushing other players and stealing their items and money in exchange for their lives.
Col can take the form of physical coins. It is currently unknown how many types of coins exist in the game.

Crystals
Crystals (結晶 Kesshō?) in Sword Art Online are considered to be one of the most convenient types of items and the closest thing to magic in the world. They have different uses, namely having immediate effect for recovery unlike potions and perform a variety of function outside of healing, extending to teleportation, corridors to locations, and displaying images or replaying voice messages.
Though extremely useful, they are expensive hence making people hesitant to use them, unless they are in very special (dangerous) situation. Most of crystals can be found through some NPC shops, except for the Corridor Crystal. Corridor crystals are the rarest of all crystals, and are only obtainable by trading with other players, or from killing monsters or obtaining them from a treasure chest.

Known Kinds
Antidote Crystal (Green) - cure any status effects.
Healing Crystal (Red) - completely heals the target.
Teleport Crystal (Blue) - transport the user to a chosen city's Teleport Gate plaza.
Corridor Crystal - a larger form of teleport crystal that opens a teleport gate to any location that the player has marked. Corridor crystals have a darker shade of blue then the teleport crystal.
Message Record Crystal - record what someone has said.
Screen-Shot Camera Crystal - take in-game screenshots.

Teleport Gate
A Teleport Gate is a feature that allows fast travel between the floors of Aincrad. It is located at the central plaza of the main settlement on each floor. The Teleport Gate allows free teleportation to any other floor where a gate is activated. This happens after the player(s) who beat the boss of the previous floor's Labyrinth opens it.

Teleport Gates have an appearance of an arch made of neatly stacked stones. It has no doors or bars. The empty space in the middle of the arch is distorted like a portal.

A Teleport Gate can be used by either standing in the middle of an active Teleport Gate or by using a Teleport Crystal, when teleporting from an area outside of a Teleport Gate, and by saying «Teleport » along with the name of the destination city.

Once a floor boss is defeated, the victorious party can activate the gate of the next floor by merely entering the main settlement and touching the surface of the portal.
This causes a blue light to spread everywhere, marking the floor accessible via teleportation to any other existing floor in Aincrad. The event is known as a «Town Opening».

In the event that the victorious party does not manage to activate the gate after reaching the floor, the Teleport Gate will automatically activate after a two hour period.

The gate can only be activated for use if the name of the destination village is known, however the players are able to check their map for the name of the village. They are also able to learn the name of the village or town from other players allowing lower level players to access higher floors.

Quest
A Quest is an NPC-initiated event that typically leads to a reward after fulfilling a series of set conditions. Certain quests are given via a bulletin board, instead of an NPC.

Last Attack
A Last Attack (abbreviated as LA), is the final strike on a monster, generally mentioned in boss fights or high level fights. A player who deals the Last Attack on monsters receives more experience and are more likely to obtain rare drops known as "Last Attack Bonus Rare Drop" rather than assists.

Duels (PvP)
Duels are authorized Player vs. Player fights that take place even in safe areas and will not change a player icon from green to orange by killing the opponent.
At the beginning of the duel, the player will have 60 seconds to prepare for the duel. After the 60 seconds end, the duel will start.

To make a duel a player must send a request to another, the second player must accept and may decide then which type of duel it will be. Once the duel starts, the AREA effect is lifted from the two duelists.
After a duel is concluded, a window that indicates the winner will appear between the participants if they are within 10 meters of each other. If the participants are farther apart at the end of a duel, then two windows will appear at the closest point to both the winner and loser separately.

Types of Duels
Total Loss Mode: Rarely used in SAO, since it will only stop when a player's HP reaches 0, and that will mean permanent death for the loser. This is the one used for Sleep PK.
Half Loss Mode: The winner is decided after the other player loses half of their HP. Rarely used in SAO since a critical hit could reduce someone's HP to the danger zone.
First Strike Mode: This is the most common, the winner is decided by whoever lands the first clean hit or whittle the opponent's HP to half.

Health Points
Health Points (HP), sometimes referred to as "Hit Points", are a standard in most games as a way of gauging how much damage a person can withstand. Once this parameter reaches zero, the character is either rendered incapacitated or dead, depending on the rules of the game.

Status Effect
A Status effect is a temporary modification to a game character's original set of stats that usually comes into play when special powers, items and/or abilities are used, often during combat. Some of such modifications have a positive effect on the character, but most of the time they are negative. Positive status effects are usually referred to as buffs, while negative effects are referred to as debuffs, which range to about 10-20 types.

Delay - The debuff received by Diabel that caused his death. Highly likely appear after continuously hit by powerful attacks.
Stun - The most common debuff that immobilises the player for up to ten seconds, and has a probability of triggering a special effect fumble, which causes the player's weapon to fall out of his hand.
Paralysis - Players affected by this debuff are rendered immobile for a long period of time. The minimum duration of the effect is 10 minutes, though the duration of the effect may be longer, depending on the strength of the attack that triggered this status.
Tumble - Humanoid monster only.
Luck Bonus - Increases luck, affects the rate of resistance towards toxic and paralysis attacks, occurrence rate of fumble and slip, and, potentially, the rate of rare drop.

Potion
A type of recovery item. The only known potions existing in SAO are healing and antidote potions, the latter being used to either gain temporary immunity to negative status effects, like paralysis, or to negate already inflicted status effects. Unlike Crystals, all potions within the game take time to manifest the desired effect and, moreover, also have a cool-down period after use, indicated by a «Cooling» icon at the bottom of the player's view, which renders drinking another potion useless until the cool-down period expires.
However, Potions can not be inhibited by anti-crystal fields and are much cheaper than Crystals, therefore they are the main type of recovery item used in a non-critical situation. Potions are usually carried in belt pouches for easy access, as taking them out of the inventory is too time consuming in the middle of a battle.

Vendor
A Vendor is where a player can buy and/or sell one's items that they have obtained in Sword Art Online.
There are both NPC and human vendors. NPC vendors have a limited range of items and set prices that are usually lower than the actual market price of the item, while human vendors can have a potentially infinite item range and prices for their items may vary. Since NPC vendors only sell a limited range of items, most of the best items and equipment are obtained though monster drops and chests on the higher floors.