From BlenderWiki

Introduction

This document describes a partial redesign of the current particle system with the following goals:

• Sustainment of current features
• Flexibility for artists
• Extensibility of code

Basics

1. Particle systems are a feature of objects (Note: it might be better to actually make particle systems an object type of their own)
2. A particle system uses a number of equal data elements ("particles"). Each particle describes a point in space with associated data, like size, mass or color.
3. Each particle in a system is treated the same way. Artists define rules for the particle set as a whole and don't have to care about individual particles.
4. Particle system configuration consists of:

   Simulation

   The change of particle attributes over time. Often includes physical simulation of particle movement, but any means of animation are possible.

   Rendering

   Can create independent render elements for each particle (e.g. halo spots), but also generate render geometry from the particle set as a whole (e.g. fluid surface).

   Display

   Realtime rendering using OpenGL primitives. Usually strongly simplified per-particle elements for performance reasons.