As you build your game, Unity stores a lot of metadata about your Assets, such as import settings and links to other Assets, among other information. If you want to transfer your Assets into a different project and preserve all this information, you can export your Assets as a Custom Package.
See PackagesPackages are collections of Assets to be shared and re-used in Unity. The Unity Package Manager (UPM) can display, add, and remove packages from your Project. These packages are native to the Unity Package Manager and provide a fundamental method of delivering Unity functionality. However, the Unity Package Manager can also display Asset packages that you downloaded from the Asset Store. More info
See in Glossary for general information on using packages in the Unity Package Manager (UPM) and Custom packages for information on creating, maintaining and deploying custom UPM packagesA Package managed by the Unity Package Manager.
See in Glossary.