Glossary
What is slippage?
In one sentence
Slippage is the difference between the price you expected and the price you actually got — most noticeable on decentralised exchanges and in thin markets.
When you place a trade, the price can move between submission and execution, or your order can be large enough to move it itself. The gap is slippage.
On a decentralised exchange this is structural. Prices come from the ratio of assets in a liquidity pool, so every trade shifts that ratio. A large trade against a small pool can execute several percent — sometimes far more — away from the quoted price.
Most interfaces let you set a slippage tolerance: the maximum deviation you will accept before the transaction reverts. Set it too tight and trades fail (while still costing gas); set it too loose and you can be badly filled. A very high tolerance also exposes you to sandwich attacks, where a bot trades immediately before and after you to capture the difference.
For example
If a token requires you to set 15% slippage to trade at all, that is telling you something about its liquidity — or about the token.