A NavMesh (navigation mesh) is a set of polygons representing where an agent can move. Instead of pathfinding over every pixel or world unit, the AI pathfinder works over connected walkable regions, which is far more efficient for 3D spaces. NavMeshes are the standard spatial representation behind many modern NPC movement systems, including Unity’s NavMesh tools and many custom AI pipelines. (Millington, Artificial Intelligence for Games, see source-artificial-intelligence-for-games; Game AI Pro 360: Guide to Movement and Pathfinding, see source-game-ai-pro-360-movement-pathfinding)
NavMeshes usually answer “where can I go?” They do not by themselves answer “where should I go?” — that still depends on decision logic, tactical scoring, and avoidance systems.
Related: pathfinding-algorithms, navigation-mesh-construction, buddy-ai, npc-performance-at-scale