BIN is an abbreviation of 'Buy It Now', an eBay listing option that lets you sell an item for a fixed price. Buy It Now was introduced by eBay as part of their endeavour to make eBay more convenient and resemble more of a traditional retail experience.
Rather than waiting for an auction to end, a buyer can use the BIN option and make an immediate purchase. Using the BIN format costs sellers an insertion fee and a final value fee, when eBay takes a commission of the sale price of the item.
Writing desirable descriptions with full information is an opportunity for potential buyers to hit that BIN button. Learn some tips on how to write item descriptions herehere