Contraction of have: we've been there.
uhv,ov, uh v,
Some Douche-bag on Urbandictionary.com thinks people are saying "of" as in "I should of" when people actually say "I should've" - meaning, I should have.
He goes on to make reference to people using English improperly for the use of this word. When the pronunciation of the word of and the contraction 've are identical.
would've is a contraction of would have.
However, many people confuse this for "would of"
This is in reference to a UB post.