A person conceived as of a man ejaculating onto a couch and a woman of knowing or non-knowing condition sitting on the couch and getting pregnant.
Based on preconceived paranoia when at drunken parties.
Based on the words Couch: a piece of furniture, and nymph: young being.
Julie: I can't believe it I'm pregnant I was even awake during the party last night.
Jim: Well are you sure it is not a couch nymph or have you been screwing Jon again?