I was on Urban Dictionary when I looked up Zutara. This is the result I got.

A ship from Avatar: The Last Airbender supporting the relationship between Zuko and Katara. Currently the most popular ship in the entire fandom (including the canon ship Kataang).
Zutara is so much better then Kataang!

My favorite definition
There is legend of a legendary ship that was so legendary it was awesome! This ship was so awesome that enemy shippers were blinded by its awesomness. Blessed by St. Jun, Prophet Iroh, and Tophgod, this epic battle ship rules the universe with its lulz, pronz, and fanon. Behold the epic ship that is ZUTARA!!
Zutara PWNS Kataang!

Zuko + Katara = Teh Ultimate Smex

There are others (most are basic information like the first one) but the last two bash the ship a bit.