a word that can be used in place of any word that you can ever think of, usually this would be a curse or bad word. Used to create funny sentences.

Genetically Engineered Life Form. Gelfs are all that remain of humanity after we render ourselves extinct in the far future, but we leave cultures of mix-matched animals on terraformed planets. Created by Rob Grant and Doug Naylor in the TV show and books of Red Dwarf.

a mythical elven creature which follows you around and is essentially a part of you

Guy Everybody Likes Friend. Commonly used by drunken party-goers on the London Underground.

G.E.L.F. =

G irls
E veryone
L ikes to
F uck

an efeminate short guy

a girlfriend (see the example below).