As part of the importing process, Unity creates metadata about any assets you import into your project. The metadata contains information such as the asset’s import settings, and where your project uses the asset. When you import an asset, Unity does the following:
The Unity Editor frequently checks the contents of the Assets folder against the list of assets it already knows about. When you place an asset in the Assets folder, Unity detects that you have added a new file and assigns a unique ID to the asset. This is an ID that Unity uses internally to reference the asset, so that it can move or rename the asset without breaking anything. You can use the Import Activity window to view the ID of an asset.
Unity creates .meta files for each folder and file in your project’s Assets folder and stores the .meta file in the same location as the asset file. These files are hidden in the Project windowA window that shows the contents of your Assets folder (Project tab) More info
See in Glossary, and are considered a hidden file by your operating system, so might be hidden by default in your file browser.
The .meta files contain the unique ID assigned to the asset, and values for all the asset’s import settings. If you change the import settings for an asset, Unity saves those new settings to the .meta file that accompanies the asset. Unity then re-imports the asset according to your updated settings, and updates the corresponding imported data in the project’s Library folder.
Meta files contain important information about how the asset is used in your project, and they must stay with the asset file they relate to. If you move or rename an asset within the Project window, Unity automatically moves or renames the corresponding .meta file. However, if you move or rename an asset outside of Unity, you must move or rename the .meta file to match.
If an asset loses its .meta file, any reference to that asset is broken in your project. In this situation, Unity generates a new .meta file for the moved or renamed asset as if it’s a brand new asset, and deletes the old .meta file. When Unity deletes the old .meta file it might cause significant issues such as the following:
.meta file, any materials that use that texture lose their reference to that texture. To fix it, you must manually re-assign that texture to any materials which require it..meta file, any GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More infoUnity assigns each folder in your project’s Assets folder its own .meta file. However, some version controlA system for managing file changes. You can use Unity in conjunction with most common version control tools, including Perforce, Git, Mercurial and PlasticSCM. More info
See in Glossary systems (VCS) can’t store empty folders. When you add or delete an empty folder from your project, the VCS stores the .meta file as added or removed, but doesn’t store the change of adding or removing the folder itself. To help resolve this issue, Unity behaves in the following ways relating to empty folders:
.meta file, it assumes another user in your VCS deleted the folder and removed the meta file, so deletes the empty folder locally..meta file for a folder, but that folder doesn’t exist locally, it assumes another user in your VCS created a new folder, and then creates a new unversioned meta file for empty folders.