The term derives from the last name of a notorious slum lord in the Santa Barbara, CA area. It has taken on the meaning of getting things the cheapest way possible, preferably free. It doesn't matter the condition or how the item looks, as long as it is at a low, or no cost. Items found in alleys, dumpsters, and on the side of the road are the epitome of the term.
"Man, I need to get a new mattress but I don't have any money. What am I gonna do?
"Don't worry about that, just pini-it. You're bound to find something in the alleys around here."