bid and ask (bid-ask prices)

The bid is the price at which you can sell an instrument (the lower of the two), and the ask is the price at which you can buy it (the higher one); the gap between them is the spread, which goes to the broker. This distinction governs order execution: a long position closes on the bid and a short closes on the ask, which is why a short's stop-loss can fire before the bid line shown on the chart reaches the level.