The 'reserve' amount refers to the lowest price that a seller has agreed to sell an item for. If the reserve is not met at the end of the auction then the seller may still offer to sell it to the highest bidder, but is not obligated to. Likewise, a high bidder is not obligated to buy the item if the reserve price is not met. Once the reserve price has been met then both the seller and the bidder are required to complete the sale.