Particle mass refers to the amount of matter contained in a particle, which determines how much it resists acceleration when a force is applied. It is a fundamental property of particles, such as electrons, protons, and neutrons, and is measured in units like kilograms or electronvolts. Mass plays a crucial role in the behavior of particles in various physical processes, including gravity and kinetic energy. In the realm of physics, mass is also linked to the concept of energy through Einstein's famous equation, E=mc². This equation illustrates that mass can be converted into energy and vice versa. Understanding particle mass is essential for studying the fundamental forces of nature and the interactions between different particles in the universe.