The mistress or side-dish in an affair. Usually associated with a cuckquean (a woman who is aroused by her male partner having sex with another woman or women).
John was out with his cuckcake while his cuckquean wife waited at home, playing with herself and waiting for all the juicy details.
A chocolate cake that has been half eaten by people who do not own it, and then the owner puts his c*ck in the remaining half before making the people eat the rest.
Joshua: Who has eaten half of my cake?
Laura,Emma,Lucy: We did.
Joshua: Well you can finish the rest, it is outside your door.
....
(the girls eat the cake)
....
Joshua: ahahahahhahahaha guess what I put in it. That's what you call a Cockcake.