In 1986 Craig W. Reynolds made a computer model of coordinated animal motion such as bird flocks and fish schools. It was based on three dimensional computational geometry of the sort normally used in computer animation or computer aided design. The artist called the generic simulated flocking creatures boids. The basic flocking model consists of three simple steering behaviors which describe how an individual boid maneuvers based on the positions and velocities its nearby flockmates.
Each boid has direct access to the whole scene's geometric description, but flocking requires that it reacts only to flockmates within a certain small neighborhood around itself. The neighborhood is characterized by a distance (measured from the center of the boid) and an angle, measured from the boid's direction of flight. Flockmates outside this local neighborhood are ignored. The neighborhood could be considered a model of limited perception (as by fish in murky water) but it is probably more correct to think of it as defining the region in which flockmates influence a boids steering.
A slightly more elaborate behavioral model was used in the early experiments. It included predictive obstacle avoidance and goal seeking. Obstacle avoidance allowed the boids to fly through simulated environments while dodging static objects. For applications in computer animation, a low priority goal seeking behavior caused the flock to follow a scripted path.
In cooperation with coworkers at the Symbolics Graphics Division and Whitney / Demos Productions, Reynolds made an animated short featuring the boids model called Stanley and Stella in: Breaking the Ice.
Since 1987 there have been many other applications of the boids model in the realm of behavioral animation. The 1992 Tim Burton film Batman Returns was the first. It contained computer simulated bat swarms and penguin flocks which were created with modified versions of the original boids software developed at Symbolics.
The boids model is an example of an individual-based model, a class of simulation used to capture the global behavior of a large number of interacting autonomous agents. Individual-based models are being used in biology, ecology, economics and other fields of study.
(source: www.red3d.com/cwr/boids)