Coven

A coven (コブン Kobun), also spelled covan (コバン koban) is a term used to a refer to a permanent gathering of two or more vampires.

Overview
A coven is formed when a vampire first finds their mate, and become bonded forever. This travelling pair of "two" is called a coven, and the function of a coven is identical to the function of any gathering of sentient creatures; it can, in fact, be considered the vampire family unit.

Covens are typically very small, most covens bordering on no more than four members, and they almost always consist of blood relations — beyond, of course, the original bonded pair. While many vampires would prefer to travel as an individual, a coven proves beneficial to a vampire as it provides them with no only companionship, but allies in case they need to defend themselves.

When rearing children, the members of a vampire coven naturally become naturally far more defensive and instinct prone, and will attack anything that proves themselves to be a threat to a young vampire child. It is an ill-advised mistake to approach a vampire coven that happens to have a young child with them.

Whilst typically consisting only of family members, it is possible for a foreign vampire to a join an existing coven.

Trivia

 * The real-life definition of "coven" refers to a gathering of "witches". As such, Guilds as the series Fairy Tail knows them, fit the technical definition of "coven" far more than the article seen here.