Coven
A group of witches who practise together. It has no fixed number, and nobody needs one.
A coven is a group of witches who meet regularly, for the full moons and the sabbats, and practise together. The word is an old Scots form of "convent" and means no more than a gathering.
It entered the history of witchcraft through the confession of Isobel Gowdie, tried in Scotland in 1662, who said that the witches were organised in covens of thirteen. In the 1920s Margaret Murray made a rule of it: every coven had twelve members and a leader. Her theory did not hold, but the number stuck. Real covens are as large as the room and the friendships allow, often between three and a dozen people.
In the initiatory lines of Wicca a coven is led by a high priestess, a high priest or both, and new members are taken in by initiation after a time of getting to know each other. Other groups are loose circles of friends without ranks.
Nobody needs a coven. Most witches are solitary, and a practice alone lacks nothing. If you look for a group, judge it as you would any other: a good one does not ask for large sums, puts no pressure on you, respects a no and has no objection to your telling friends and family where you are.
Related: Wicca in brief, etiquette among witches.