What are all the storage categories that can exist?

Solution 1:

The System Information User Guide (also available on your Mac as a macOS Help article) gives an overview of the categories available in the Storage section of the About My Mac window:

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Apps: Contains all the apps installed on your Mac (excluding system applications).
Documents: Contains files in your home folder that aren’t included in other categories, such as Pages documents and PDFs. It also includes videos and photos that are not managed by your photo library (for example, an image that a friend shares with you using AirDrop).
iCloud Drive: Contains all files stored in iCloud Drive. It may also contain files in your Desktop and Documents folders if you store them in iCloud Drive.
iOS Files: Contains iOS backups and firmware.
TV, Music, Books, and Podcasts: Each app category contains purchases from that specific app, which can be removed from your Mac and downloaded again.
Mail: Contains emails and attachments.
Messages: Contains content from Messages conversations, including attachments.
Music Creation: Contains content from GarageBand, Logic, and MainStage.
Photos: Contains your System Photo Library.
Trash: Contains items you deleted (items deleted from iCloud Drive are not included in the amount of storage space).
Other Users: Contains files created and modified by other user accounts on your Mac.
Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.
System: Contains macOS system applications and files. Examples include Mail, Terminal, Calculator, and Time Machine Local Snapshots.