Pricing and rates
Slippage
The gap between the expected price and the executed price, caused by limited order book depth.
A large order does not execute at a single price: it consumes the best available offers, then the next ones, which are less favourable. The average price obtained therefore diverges from the price displayed when the order was sent.
Slippage depends on the traded pair’s liquidity, not on the absolute order size. Selling ten thousand currency units of bitcoin moves nothing; the same amount in a thinly traded asset can move the price. That is one reason illiquid corridors carry a surcharge.