Artificial Intelligence

An NPC, meaning non-player character, is a term used when talking about characters or creatures in a video game controlled by a computer. They can be enemies, allies or just people walking in the streets. 

This is an example of some enemy and civilian NPC’s from Assassin’s Creed.
NPC’s require specific data to move intelligently, find hiding positions [...]

Animation Systems

The disadvantages of a mesh based character system is that you have to move and define the position of every point on a model. This many vertices and polygons can become a lot for a computer to handle.
The advantages of skeletal animation are that instead of moving each point of the mesh individually, you move them [...]