Market Impact
How far your own order moves the price, separate from the spread you cross to get filled.
Market impact is the price move your order causes by consuming liquidity, which is not the same thing as slippage. Slippage is the gap between the price you expected and the price you got, and it includes the spread and any delay. Impact is specifically the part you caused: a market order walks the book, each level fills at a worse price than the last, and the book takes time to refill. Impact scales sub-linearly with size in most markets, so ten times the size costs far more than ten times the spread but much less than ten times linear. The only honest way to know your cost is to walk the current book rather than assume, which is what our ladder does: it prices market orders from 10 thousand to 5 million USD against the live depth for eight major perpetuals.