Adj. The act of searching through a room that houses miscellaneous unwanted items in order to find something for yourself. Originating in the Berkeley Cooperative System, the term specifically refers to hunting through the "free pile room" where old co-opers leave their unwanted items to avoid clutter in the moving process.
"Sweet, I just found a pair of mannequin legs while free-pileing that I can put in my room!"
"I need a costume for the co-op party. Time to go free-pileing!"