Epistrepho means to turn, to turn around, to return to a previous state, or to convert. It can describe physical turning (turning one's head, turning to face someone) or the radical spiritual turning of conversion — turning from idols to the living God, turning from sin to righteousness. It is the NT's primary word for conversion in Acts.
In Acts, epistrepho describes the missionary moment: Gentiles 'turning to God from idols' (Acts 14:15, 1 Thess 1:9). This turning is both the abandonment of false worship and the embrace of the true God. Peter calls Israel to 'repent and turn [epistrepho]' for the refreshing of the presence of the Lord (Acts 3:19). The Great Commission ends with making disciples — the ultimate epistrepho: people turning from all other loyalties to King Jesus. The word is also used for Peter's restoration: 'when you have turned back [epistrepho], strengthen your brothers' (Luke 22:32).