When you create a market order, the order fills at the best available price, which means that an order will keep being filled from an order book until the entire order is executed. However, if there is not enough liquidity around the desired price to fill a market order, there could be a larger difference between the price you expect to fill and the price the order fills at. For example, if you were to buy 100 BTC from an exchange, your slippage might be quite high, especially if the exchange does not have a lot of BTC in their liquidity pool. In an ideal world, your slippage would be near 0%—this means your order fills at your desired price. However, if your slippage is high at say 15%, you’d likely receive up to 15% less tokens when you submit your order due to lack of liquidity.