Limit order
In short A limit order buys or sells at a price you set or better and waits until the market reaches it. You control price, but a fill is never certain.
A limit order is an instruction to buy or sell an asset only at a price you choose or better. A buy limit fills at your price or lower, and a sell limit fills at your price or higher. If the market never reaches that level, the order just sits there unfilled.
On a centralized exchange, your order goes into an order book, which is a list of resting buy and sell orders. It waits until someone on the other side accepts your price, and it can fill completely, partially, or not at all. Most decentralized exchanges built on automated market makers have no order book, so they have no native limit orders. Some platforms add the feature with a keeper bot or aggregator that watches the price and submits a swap for you once your target is hit, and a few chains do run true on-chain order books.
The main reason to use one is price control. A market order takes whatever price is available right now, which on a thin small-cap token can mean a poor fill with heavy slippage. A limit order caps what you pay or sets a floor on what you receive, and on centralized exchanges a resting order can also qualify for lower fees. The tradeoff is that execution is never certain.
Watch for a few traps. Price can gap past your level without filling you, or touch it briefly and fill only part of the order. A sell limit placed below the current price simply fills right away at the best available price, so it does not protect you from a drop; that job belongs to a stop order. With DEX limit tools, check who holds your funds while the order is open, how it gets executed, whether it expires, and what fees the service takes. Also remember that a fill is not proof the price was good, since a limit buy in a falling market often fills just before the next leg down.