The Bid Price is the highest price which prospective buyers are willing to pay in the market. It can be considered the highest price at which you can currently sell your shares in the market. It is quoted in the same units as the quoted price.
The Bid Price should be contrasted with the 'Ask' Price which is the price that sellers are asking.
Note that the Bid Price is generally often lower than the Last Price and the Ask Price. Sellers can only sell at lower prices than buyers can buy. The difference between the Bid and Ask is known as the Spread.