Crowd simulation
Simulating the movement of many agents at once so they reach their goals without walking into each other or clumping up.
The problem splits into two layers. Global routing is handled by a navmesh or a flow field pointing toward the goal; local avoidance keeps agents from colliding moment to moment. The most common local method is Reciprocal Velocity Obstacles and its successor ORCA (van den Berg et al., 2008), where each agent picks a velocity that avoids collision on the assumption that neighbours share half the responsibility.
The root is Craig Reynolds's boids (1987), and the technique spans games — the crowds in Assassin's Creed — to film, where the Massive software animated the armies in The Lord of the Rings (2001), on to building evacuation analysis. Steering behaviors often sit underneath for the movement itself.