In the past, a cuckold was simply a man whose wife had an open affair behind his back, whilst he did nothing about it.
These days most cuckolds are willing and happy participants in fantasy games played by him and his wife.
These games can take many forms and are usually based around the idea that the wife is punishing her husband for being a poor lover or having a small endowment.
What usually happens is that the wife will either play with her lover in front of her husband, or go out and have sex with one of her lovers, then come home and tell her husband what she has been doing while they make love.
There are also several Sub Cultures in the cuckolding scene, involving pregnancy, interracial sex, forced bi-sexuality