Any-angle pathfinding
Pathfinding that allows edges in any direction instead of forcing the route onto the grid's 45- and 90-degree lanes.
Classic A* on a grid can only step to neighbouring cells, so the path zig-zags along eight compass directions even across open ground where a straight line would be shorter and more natural. Any-angle algorithms break that by letting a waypoint see past intermediate cells: if there is line of sight from A to C, B is dropped.
Theta* (Nash et al. 2007) runs the sight check during the search itself; Field D* and Lazy Theta* trade accuracy for speed. The alternative is to run plain A* and "string-pull" the path afterwards, but that can miss shortcuts an integrated search finds. The result is straighter, less robotic routes — most visible for vehicles and flying units.