The Greek alisgēma means pollution or defilement — specifically the contamination associated with idolatrous worship. It appears in the decree of the Jerusalem Council (Acts 15:20, 29).
The Jerusalem Council's letter to Gentile believers asked them to abstain from "food polluted by idols" (alisgēmata) — reflecting the real pastoral challenge of the early church in a world saturated with idolatrous temple worship. This was not salvation by works but a call to boundary-marking holiness that would facilitate fellowship between Jewish and Gentile believers. The deeper principle: the redeemed are not to be defiled by participation in the idolatrous system from which they have been liberated.