Bid-ask spread

On a given exchange and trading pair, the bid is the highest price any buyer has posted, and the ask is the lowest price any seller has posted. The spread is the gap between them, often shown as a percentage of the midpoint so you can compare tokens at very different prices. The same token can have different spreads on different venues, and in different pairs on the same venue.

A market order takes liquidity from the order book. A small market buy fills at the ask and a small market sell fills at the bid, so buying and immediately selling costs roughly the spread plus fees, even if the price never moves. A larger order can eat through several price levels, so your average fill ends up worse than the best quote.

On a DEX built on an automated market maker, there is no order book and no literal bid and ask. Your cost shows up as the pool fee plus price impact, which grows with your trade size relative to the pool's reserves. Thin liquidity still hurts, because a large buy gets a poor price and a later exit can be expensive.

A limit order gives you control over price, but a resting order might never fill if the market moves away. One priced at or through the ask executes immediately and pays the spread, just with a cap on how much worse the fill can get.

Charts usually show the last trade or a midpoint, not a price you can actually get. Before buying a small token, check depth on both sides of the book on an exchange. On a DEX, quote a small and a larger buy and sell, and compare them against pool size and fee tier. Be wary of a tight spread with almost no depth behind it, since spreads widen fast during sharp moves. If buys work but sells fail, that is a common honeypot sign.