Bid-offer spread
The gap between the price at which currency is sold to a client and the price at which it is bought back.
How to read the number
This is the cost of getting in and out: a trade starts at a loss the size of the spread, and that has to be recovered before any profit.
When the metric lies
The spread widens outside the main session and during violent moves, which is exactly when the urge to transact appears.
Also known as: dealing spread