Cuckoldry is sexual infidelity committed by a female to her boyfriend or husband. A male cuck is someone who allows his wife to cheat, someone who engages in polyamory, or someone who is not able to sexually satisfy their partner (leading to cheating by the female).
Most incels don't use this word as a pejorative, but for those who do, it's odd because incels in general are not able to get a woman at all, which is the first step to pleasing a woman sexually.
Some females get off by participating in quasi-cuckoldry. This involves having casual sex with a slayer, right before dating a beta provider or right before committing to a beta provider. This leaves the beta provider a risk of providing for the child that's not his own. Lying about her past experiences with other men is another form of quasi-cuckoldry. (See also Slutting it up with the slayers)
Slayers also get off by participating in quasi-cuckoldry. This involves hiding the identities of the females he has had sex with. Later when the females find their own boyfriends, they would be unaware of her past sexual experiences. The slayer will get off at the thought of their boyfriends providing for them (who used to gave him sex for free).
Wittoldry is similar to cuckoldry except in relation to family; i.e. example someone who welcomes random strangers to bonk their immediate family. A man who behaves this way is a "wittold". A woman who behaves this way is called a wittoldress or wittoldatrix. The act in and of itself is called "wittolding", while its verbified form is "wittoldize" or "wittoldizing".