Slippage
The gap between the price you expected and the price your trade actually executed at, caused by thin order books or fast-moving markets.
Slippage is the difference between the price on your screen when you placed a trade and the price you actually got. It is not a fee anyone charges. It happens because the market moved, or because your order was bigger than the amount on offer at the quoted price.
A worked example. An order book offers 5 coins at £100 and the next 5 at £101. A market buy of 10 takes both levels: the average comes out near £100.50 against the £100 you saw, which is 0.5 per cent of slippage. Nothing malfunctioned. The book ran out of coins at the first price.
Slippage bites hardest in small, thinly traded tokens, during volatile moments, and on large orders. Decentralised exchanges ask you to set a slippage tolerance before a swap, the worst rate you will accept, and the trade fails if the pool moves past it.
Buying through a quoted-price service works differently: the number shown is locked for a short window, so the price you approve is the price you pay. Our full guide on slippage walks through the mechanics and the ways traders reduce it.