What is reset in bowling?

Answer 1

The reset button is a way to manually trigger the sweeper if your ball doesn't do it automatically.

On the first shot of a frame, the reset button triggers the pinsetter to pick up any pins still standing before the sweeper clears the deck.

On the second shot of the frame, the reset button triggers the sweeper to clear the deck and the pinsetter to set a new rack of ten pins.