Particle systems are a method used in 3D computer graphics to simulate certain environmental effects such as rain, explosions, and smoke.
A particle system is made up of particles. A particle is a small object with properties such as position, velocity, and color. Typically, each particle is textured and rotated to face the viewer (called billboarding). Particles are produced at the desired location by an emitter.
A particle system has its own rules that it applies to every particle. Often these rules involve interpolating values over the lifetime of a particle. For example, many systems have particles fade out to nothingness by interpolating the particle's alpha value while the particle is active.
Particle systems can be created and modified in some 3D software including 3D Studio Max and Maya. These editor programs allow artists to have instant feedback on how a particle system might look given properties and rules that they can specify. There are even programs that make particle systems work better, such as AfterBurn and RealFlow (for liquids).
