What is the slingshot effect of a magnet?

Excuse me, could you please explain in simple terms what the slingshot effect of a magnet is? I've heard about it in relation to certain types of propulsion systems and I'm curious to understand the underlying principle behind it. Is it something related to the force generated by the magnetic field, or does it have to do with the movement of charged particles? I'd appreciate it if you could provide a concise yet informative answer to help me grasp the concept better.