The lowest price at which someone is willing to sell the security. When combined with the bid price information, it forms the basis of a stock quote.
The highest price a buyer is willing to pay for a stock. When combined with the ask price information, it forms the basis of a stock quote.
A two-way price quotation that indicates the best price at which a security can be sold and bought at a given point in time. The bid price represents the maximum price that a buyer or buyers are willing to pay for a security. The ask price represents the minimum price that a seller or sellers are willing to receive for the security. A trade or transaction occurs when the buyer and seller agree on a price for the security.
The difference between the bid and asked prices or the spread, is a key indicator of the liquidity of the asset - generally speaking, the smaller the spread, the better the liquidity.
The bid-ask spread can widen dramatically during periods of illiquidity or market turmoil, since traders will not be willing to pay a price beyond a certain threshold while sellers may not be willing to accept prices below a certain level.