Cuckold,  by simple definition is a husband with an unfaithful Slut Wife - the cuckold husband could be willing or unknowing.

Cuckolding is "the act" of making a husband into a cuckold.

In terms of a femdom lifestyle or D/s, cuckolding  is not simply about a Slut Wife going out to have sex with other men.  It's a mind screw of the cuckold's psyche and the Slut Wife makes him a cuckold with his knowledge.
The cuckold husband needs to be turned on or have other needs being met, such as being humiliated, dominated or simply being able to see his Slut Wife have an orgasm that for some reason he is not able to give her.