the temple: the whole sacred building and its surrounding courts, the place set apart for God
This word names the temple as a whole place, the entire walled complex with its courts, porches, and treasury, not just the small inner room where God was thought to dwell. That is why people walk in it, teach in it, sell animals in it, and are arrested in it: the word covers the wide public grounds where crowds gathered, where Jesus taught daily, and where the apostles met.
Almost every time it appears it means the temple in Jerusalem, the center of Israel's worship. Once, in Acts, it names a pagan temple instead, the great shrine of the goddess Artemis at Ephesus. The core idea does not change: a building and grounds set apart as holy to a god. Only the god is different.
The contrast with the other Greek word for temple matters. Where this word means the whole sacred precinct, the other word names just the inner sanctuary, the holy house at its heart. Keeping them apart explains how Jesus can be teaching in the temple courts and yet never enter the inner shrine, which only priests could approach.