Final answer:
A piston-cylinder system is classified as a closed system, which means it can exchange energy, but not matter, with its surroundings.
Step-by-step explanation:
A piston-cylinder system can be classified as a closed system. A closed system is a system that can exchange energy, but not matter, with its surroundings.
In the case of a piston-cylinder system, the gas inside the cylinder is enclosed by the cylinder walls, so it does not exchange matter with the surrounding environment. However, energy can be transferred in the form of work during compression or expansion of the gas.