Cuck is short for cock held.
This is a man who is in a domanate realashonship with with a women.
Man 1:Hey do you know steve?
Man 2: what the cuck?
Man 1: yeah him
A man who hit on your girl while she is with you. He will do anything to smash her while your dating her. They also let the girlfriends do whatever they want and cucks wouldn't even care if there girlfriend smashed another guy in front of them.
Woah, Kyle tried to sleep with your girlfriend? What a cuck!
A cuck, short for cuckold, is a well known fetish where one person in a relationship engages in coital activity whilst the other watches.
For example;
Lloyd: “hey i got cucked pretty back last night”
Dan: “what happened bro?”
Lloyd: “my gf fucked you, remember?!”
Average fan of NTR, or Netorare hentai
“There is so much NTR hentai on hanime”
“Seriously. There is so many cucks”