Collective Magic is a powerful form of witchcraft constantly shown by the Bonum Coven throughout the book series. This connects and pools powers and strength of the members of a coven together, allowing them to become stronger and perform amazing feats of witchcraft without exhaustion. Collective Magic is unique to the particular coven, meaning that the strength of the members defines their collective strength together, such as the Bonum Power.
Some covens gain the collective ability of telepathy and the leader is able to manifest forms of sensing.
A downside of Collective Magic, which is present without it being channeled, is that if one member dies, the remaining become weaker.
Collective Magic is passed down through generations of covens, but instead of the power being taken away, the previous coven's power simply grows fainter.