OneDrive - Tags / Labels

While not exactly what you are asking about, you can create Labels in the O365 Security and Compliance center that can be used for a variety of purposes, see https://support.office.com/en-us/article/Overview-of-labels-af398293-c69d-465e-a249-d74561552d30 for the details.

Another option is to use Azure Information Protection to provide users the ability to classify and label documents. This will provide your organization the ability to control the use of files when they are shared or removed from the system, see https://docs.microsoft.com/en-us/information-protection/understand-explore/what-is-information-protection for some more info.

MS is currently working on consolidating/integrating these 2 labeling techniques.

Custom search pages can be created to make it easy to find files that have these types of labels