Animation System: "Unity has a rich and sophisticated animation system (sometimes referred to as ‘Mecanim’). It provides:
- Easy workflow and setup of animations for all elements of Unity including objects, characters, and properties.
- Support for imported animation clips and animation created within Unity
- Humanoid animation retargeting - the ability to apply animations from one character model onto another.
- Simplified workflow for aligning animation clips.
- Convenient preview of animation clips, transitions and interactions between them. This allows animators to work more independently of programmers, prototype and preview their animations before gameplay code is hooked in.
- Management of complex interactions between animations with a visual programming tool.
- Animating different body parts with different logic.
- Layering and masking features"

Animation Clips: "Unity’s animation system is based on the concept of Animation Clips, which contain information about how certain objects should change their position, rotation, or other properties over time. Each clip can be thought of as a single linear recording. Animation clips from external sources are created by artists or animators with 3rd party tools such as Autodesk® 3ds Max® or Autodesk® Maya®, or come from motion capture studios or other sources."

Animation Controller: "Animation Clips are then organised into a structured flowchart-like system called an Animator Controller. The Animator Controller acts as a “State Machine” which keeps track of which clip should currently be playing, and when the animations should change or blend together.
A very simple Animator Controller might only contain one or two clips, for example to control a powerup spinning and bouncing, or to animate a door opening and closing at the correct time. A more advanced Animator Controller might contain dozens of humanoid animations for all the main character’s actions, and might blend between multiple clips at the same time to provide a fluid motion as the player moves around the scene."

Avatar: "Unity’s Animation system also has numerous special features for handling humanoid characters which give you the ability to retarget humanoid animation from any source (for example: motion capture; the Asset Store; or some other third-party animation library) to your own character model, as well as adjusting muscle definitions. These special features are enabled by Unity’s Avatar system, where humanoid characters are mapped to a common internal format."

Animation Component: "Each of these pieces - the Animation Clips, the Animator Controller, and the Avatar, are brought together on a GameObject via the Animator Component. This component has a reference to an Animator Controller, and (if required) the Avatar for this model. The Animator Controller, in turn, contains the references to the Animation Clips it uses."

Recommended Tutorials:
Unity Learn Animation Tutorials (check the "Animation" topic to filter tutorials): https://learn.unity.com/tutorials

Unity Timeline: "Use the Timeline window to create cut-scenes, cinematics, and game-play sequences by visually arranging tracks and clips linked to GameObjects in your Scene.​​​​​​​"
Unity Learn Timeline Tutorial Page: https://learn.unity.com/tutorial/timeline#
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