Slippage is the gap between the price you were quoted and the price you got: your own trade moving the pool, or the pool moving between quote and execution. On thin liquidity a large order trades against itself, buying its own price up.
The defenses are routing and tolerance: splitting the trade across pools and venues so no single pool feels the size, and setting a slippage tolerance above which the transaction reverts rather than fills badly. A revert costs gas; a bad fill costs the difference forever.
Slippage is the difference between the price you expect and the price your trade actually gets. In pool-based trading it comes from the curve: your own trade moves the ratio, so the average rate you receive is worse than the mid price you saw. The bigger the trade relative to pool depth, the larger the gap.
Two other sources exist. Latency slippage happens when the market moves between quote and execution, which is worse on volatile assets and slower chains. Sandwiching is the adversarial version: someone sees your pending trade and places orders around it to harvest the move your size creates.
The mitigations are mechanical. Aggregated routing splits trades across pools so no single ratio moves much. Quotes bind to a maximum slippage you approve, reverting the trade if exceeded. And final-amount previews put the number in front of you before the signature, which is the last line of defense.
A large swap of a thin token might show 0.8% expected slippage in the preview against a deep USD pair's 0.02%. Approve both knowing the numbers, or split the thin trade into two legs, and the effective cost falls accordingly.
The swap shows expected output, route, and tolerance before you sign, and the router splits across venues to keep the executed price at the quoted one.
For merchants the exposure is on the conversion side: receipts auto-converting from volatile assets into the settlement token ride the same curves. Checkout quotes bind slippage at the buyer's signature, so the invoice amount is protected; treasury moves can be timed and split to keep costs flat. A closing note on expectations: slippage is not a defect to be engineered away but the honest cost of size meeting finite liquidity. The systems that treat it well are the ones that surface it, bind it, and let you split around it, which is precisely what the preview, the tolerance setting, and manual leg-splitting are for. A platform that never shows you slippage is not eliminating it, only hiding where it lands.
Every term behind the rails, the assets, and the settlement.