Q. Do all witches belong to covens?
A. Sometimes the whole 'coven' concept is brushed aside as a stereotype, but many witches or Wiccans do belong to groups that we call covens. But it is definitely not necessary or required to be in a coven in order to be a witch.
Some traditionalists say that you do need to belong to a coven in order to refer to yourself as Wiccan, but it's becoming more and more accepted that Wicca can be practiced alone just like witchcraft itself.
People who do not belong to a group are called 'solitaries'. Also, covens do not have to have 13 members, nor do covens always gather on full moons. Coven arrangements are quite variable and can range from a very structured group, to a loose and informal group.