A nickname Transformers fans use for each other, coming from "Transformers Fan". It is somewhat a term of endearment. Female Transfans seem obsessed with Starscream.
Not to be confused with Wikipedia's definition.
"Yeah, I collect the action figures, I've been a transfan for years."
"There's this other transfan I know on Seibertron.net who loves Astrotrain too! SQUEE!!"