Local commuter train. When checking tickets, conductors take your ticket and instead pin a slip of paper with your exit station marked on it.

One or two stops before your exit, they'll take that slip back. Which means they won't come back before your stop.

If you didn't manage to buy a ticket at the station, you can pay the conductor. +5$ for the conductor's service. You only don't need to pay this extra fee if it was impossible to buy a ticket at the boarding station.