The bid-ask spread Expression used to indicate the difference (called the spread) between the spot selling price (ask) and the spot buying price (money) of listed financial assets. In the Anglo-Saxon context, it is known as the bid-ask spread.
The origin of this expression dates back to the time of the first stock market trading, towards the middle of the 16th century. Those who, in fact, sold debt securities, goods, or foreign currencies offered the buyer the l., Or the paper document proving the possession of the asset and the exchange operation, while those who bought offered the d. (the price of the purchased goods). The two terms then spread into common language maintaining the same meaning: the d. represents how much the intermediary (a bank or a market maker) is willing to pay for the purchase of a certain financial asset, while the l. what the intermediary requires for its alienation.
The difference between the two prices is called the bid-ask spread. Wanting to give an example, assume that on a certain date the d.-l. euro/dollar is equal to 1.4448 / 1.4452; this means that it is possible to sell a euro to the intermediary at the price of 1.4448 dollars (purchase price by the money intermediary) and buy it at 1.4452 dollars (sale price by the intermediary-letter), with a spread of 0.0004 (0.04%). In particular, the spread is measured in basis points ( basis points, bp).
The basis point is an indicator used in finance with the following convention: 1 bp = 0.01% or 100 bp = 1%. Therefore, in the example, the spread d.-l. amounts to 4 bp. As you can see, the difference between the two prices is minimal. This usually occurs for underlying characterized by a large number of transactions and conspicuous trading volumes, connected to the high competition present on the market. Often, in fact, the measure of the d.-l. it is used as an indicator of market liquidity and also as a basis for transaction costs, which normally include this spread and the various brokerage fees.