A mass-spring system consists of a mass attached to a spring, which can stretch or compress. When the mass is displaced from its equilibrium position, the spring exerts a restoring force that tries to bring the mass back to its original position. This interaction creates oscillatory motion, where the mass moves back and forth around the equilibrium point. The behavior of a mass-spring system can be described using Hooke's Law, which states that the force exerted by the spring is proportional to its displacement. This system is a fundamental example in physics, illustrating concepts like simple harmonic motion and energy conservation.