Shortened form of "definetly possibly". Since anyone that says "definetly possibly" sounds like a complete fool, someone came up with "def poss". Doesn't really save
much time in speech, but it does save
a person's reputation. The advantage of saying "def poss" as opposed to "possibly" or even
"poss" for that matter is the fact that "def poss" implies
that is a serious possibility, rather
than someone just teasing with a half-hearted "possibly".