The price at which a market maker will buy a security which could be shares, warrants or, in the case of unit trusts, the price at which units will be bought back from their holders. Bid prices for shares are quoted on the London Stock Exchange SEAQ system, and displayed live on brokers computer screens. The prices are only firm for quantities within the normal market size of a stock, limiting the ability to sell a large quantity of shares in, for example, a small AIM stock.