Two-Pole Circuit Breakers
Two-pole circuit breakers are used with 240-volt circuits. The NEC requires two-pole breakers for two hot wire circuits. If there is a short circuit to either hot wire, both poles are grouped together so the breaker will trip.
If you were to wire a 240-volt circuit using two single-pole breakers, a short to one of the hot wires would only trip one of the breakers. The other branch circuit would remain energized and this is not safe. An electrician can confuse a branch circuit for being off and could get electrocuted.