Slippage happens when the market moves between the moment an order is placed and the moment it executes, or when the order is large enough to walk up (or down) the liquidity available at a given price. In meme-coin markets, slippage can be severe for thinly traded pairs. Traders usually set a slippage ceiling — a maximum tolerable deviation — so that if the price moves beyond it, the trade cancels instead of filling at a bad level.
Glossary
Slippage
The difference between the price you expected on a trade and the price it actually filled at.