Pathing

From The StarCraft 2 Wiki

Pathing is the programming units have in order to know how to move around other units and obstacles in the terrain.

All units or buildings in the game that can move have a dedicated pathing, which decides how the unit should react when it meets an object or another unit. In StarCraft I, the pathing was quite poor, and two units meeting in an open field on direct "collision" might spend several seconds to decide how to pass each other and continue on their way. In WarCraft III this is significantly improved and even more so in StarCraft II.

Good pathing improves efficiency, as the unit will spend more time doing its task rather than moving around. In StarCraft II, they decreased the number of minerals any given worker can carry, because the improved pathing made them so much more efficient over all. Units such as Zealots or Zerglings also increase efficiency, as their ability to fast find their target to start hitting them is vital in melee. This can be called the "micro" part of pathing, and also decreases the need to microing.

The opposite, or "macro" part of pathing is units able to find the most efficient route around large obstacles in a map, or a nunit able to find his way out of a "labyrinth" in the terrain.