It is an auction term. BIN = Buy It Now. In case, an seller puts in a BIN price in an auction, any buyer bidding the BIN price wins the auction. The seller will stop accepting bids if BIN price is reached. A seller usually put a BIN price a little higher than what he thinks is the fair value of the item.
Its Buy it now ....You can place your bid if anyone wants to sell his item and you are interested in buying that thing.