For questions related to the pricing details of securities in markets where there exists the notion of "resting orders" or an "order book".

The bid–ask spread (also known as bid–offer) for securities is the difference between the prices quoted (either by a single market maker or in a limit order book) for an immediate sale (bid) and an immediate purchase (ask). The size of the bid-ask spread in a security is one measure of the liquidity of the market and of the size of the transaction cost.

Source: Wikipedia