A small protrusion that juts away from the main body of a thing. Often used when referring to part of a character's Loaf that protrudes out.
Originally from the discussion around the episode "Conspiracy", where parasites attempted a takeover of Starfleet, but were detectable via a small protruding gill on the back of the neck of the infected. This has led to a call to "check for nubbins".
Ben told the viewers and Adam about a protruding but small chest nubbin he had during the recording of the pod. As of now it is assumed to be benign and possibly cured. Ben is not trying to take over Starfleet as far as anyone knows.
"Nubbin" is not, and this cannot be stressed enough, the setup for a dick joke. No matter how much it sounds like one when you think about it.
Correct usage: "They really went to town on the loaf - some great nubbins there."
Incorrect usage: "Riker wants to show her his nubbin. If she's consenting, of course."