Decline from a standard level of performance or achievement WordNet 3.0 & Open English WordNet

With regard to futures contracts as well as other financial instruments, slippage is the difference between where the computer signaled the entry and exit for a trade and where actual clients, with actual money, entered and exited the market using the computer’s signals. Wikipedia

The difference between estimated transaction costs and the amount actually paid Wikipedia Disambiguation

Difference between estimated transaction costs and the amount actually paid Wikidata

The difference between estimated and actual transaction costs. Wiktionary