Unity uses four different rig configurations:

• Generic rig: This one is used for quadrupeds, spiders, and other non-humanoid characters. It uses Unity's Mecanim system for controlling animation flow. It can use root motion if you provide a Root node—a bone responsible for character movement.
• Humanoid rig: This one is used for humanoid characters only. It also uses Mecanim system for controlling animation. If you are using Humanoid rigs, you have more options for importing animations. The biggest advantage is automatic animation retargeting—you can use the same animation clip on various types of humanoid characters (for example, a dwarf and a troll).
• Legacy: This option is used mostly for backward compatibility with previous versions of Unity. It is similar to the Generic rig but uses scripts instead of Mecanim for controlling animation flow. I recommend using Generic rig instead.
• None: This last option turns off the rig and disables animation import.

We will discuss differences between Generic and Humanoid rigs further in the next recipe.