Kinktionary
More like guidelines and a lot less like definitions.
Cuckolding
A form of humiliation or voyeuristic play where a cuckold or cuckquean is allowing their partner to engage in sexual activities with another person. Sometimes the concept is that the other person takes on the role of a Bull or a Cuckcake. The focus of the play often tends to be that the other person is more sexually potent than the cuckold or cuckquean but it can also just be for the voyeuristic and exhibitionistic pleasure of all parties.
The sexual engagement of the Cuckoldress or partner of the cuckold / cuckquean usually happens with the knowledge of all parties, but may not necessarily include all people in the sexual activity itself. There are gentle variations that have the cuckold or cuckquean just being aware of the sexual activity taking place. Often the cuckold or cuckquean is actively humiliated by the people engaging in the sexual acts this can include things like requiring them to cleanup bodily fluids after the sexual act is finished.