Terminology

Asset - A source file on disk, typically located in the Project’s Assets folder. This file is imported to a game-ready representation of your Asset internally which can contain multiple Objects.

Object - A single Unity serializable unit. All Unity Objects derive from UnityEngine.Object. An imported Asset is made up of one or more Objects. For example a ScriptableObject Asset has a single Object, while a Prefab contains a heirarchy of GameObjects, Components and other Unity Objects.

SubAsset - An additional Asset that is stored inside an Asset file. See AssetDatabase.AddObjectToAsset and AssetBundle.LoadAssetWithSubAssets.

Includes - The set of Objects from which an Asset is constructed.

References - The unique set of Objects that are needed (referenced) by the Includes of an Asset, but not included in the Asset. For example a Material object inside a Material Asset can reference a Shader object inside a Shader Asset.