Market order

A market order fills against whatever limit orders are already sitting on the book, starting at the best price and working outward until the whole order is filled. That means it always executes (as long as there's any liquidity), but the average price you pay can differ from the price you saw right before clicking.

For example, buying $10,000 worth of an asset where the first $6,000 of asks sit at $60,000 and the next $4,000 sit at $60,050 fills at an average price of about $60,020 — $20 worse per coin than the quoted price, purely from working through the book.

A common mistake is using market orders on thin, low-liquidity pairs, where even a modest order can walk through several price levels and cost far more in slippage than the trading fee itself.