Pixie Pasha
So a solitary witch would be some one that was initiated into a Wiccan coven but chooses to practice alone?
No. All Wiccans are witches, but not all witches are Wiccan. As Esselean pointed out, witchcraft and Wicca are not synonymous terms. A person can be a witch, without being a Wiccan, and it's perfectly acceptable to call ones' self a solitary witch if you work alone. Wicca as a religion incorporates witchcraft as part of its' practice - hense why all Wiccans are witches - but without initiation into the Mysteries, a witch is not a Wiccan.
Since that practice is also coven-based, even an initiated Wiccan cannot practice Wicca by themselves. Outside the context of the coven, the rites make little sense and in some cases aren't possible to perform solo.
The only real 'solitary' Wiccan is an initiate who may be separated from their coven by distance, illness, a move, etc. and isn't able to worship with them. Even in such a case - they are still Wiccan, because they are an initiate, but what they do on their own isn't Wicca.
Example: When I perform ritual at home, alone, I am technically performing neo-pagan ritual. Although those rituals still have a good deal of Wiccan 'flavour' to them, I wouldn't, and don't, call them Wicca; it's very different from working with a coven. I still do solitary work - sometimes weather cancels a coven meeting, and l feel that working alone is important and fufilling, and sometimes working alone is required by my training. But it isn't the same as the core rites, and I don't pretend that it is.