Legacy Animation system

Unity’s Legacy animation system (Legacy) has a limited feature setA feature set is a collection of related packages that you can use to achieve specific results in the Unity Editor. You can manage feature sets directly in Unity’s Package Manager. More info
See in Glossary that predates Mecanim. Legacy is still available because it is easier to use and provides better performance for simpler animations.

Additional resources

• Animation tab
• Importing a model