A greeblie is-
1. Any item that, when added to a construct, transforms it into something that appears to belong in a sci-fi setting
2. A weird looking sci-fi creature used to promote one’s own web site
Greeblies.com sells accessories to help the sci-fi modeller create the ship they want from “that mass of styrene sheets, ping-pong balls, VCR bits, blood, sweat, and maybe even a few tears” that’s lying around begging to be kitbashed.