Tags 

Tags are assigned to entries and assets on an environment level. They help users to organize and search for the content within the web app.

Tags are especially helpful if you have multiple teams of contributors working together within one space. Tags can help editors quickly and easily identify which content is most relevant for them.

According to their visibility, tags are divided into two types: private and public. Private tags can only be viewed by users with relevant permissions. Public tags are visible in an environment, as well, but they can also be returned to your client-side apps via the Content Delivery API. This is especially useful if you want to group content no matter the content type and query for these grouped entries or assets from your applications. Use private tags for organizing content within the web app or public tags for organizing content in your applications. By default, tags are always private.