Best bid and offer
The highest price among buy orders and the lowest among sell orders standing in the book at this moment.
How to read the number
These are two prices, not one. A market buy meets the best seller and a market sell meets the best buyer, so entering and leaving in the same second happens at different prices.
When the metric lies
The best price shows only the top of the queue. The size behind it can be tiny, and the remainder of an order walks into the levels above or below.
Also known as: bbo