Page History

...

Because labels are user-defined, you can add any word that helps you identify the content in your site.

Below the basics for label usage is explained,  if you want to know more read the following Atlassian page: Add, Remove and Search for Labels and Display Pages with Label Macros.

Label a page or blog post

Any user with permission to edit a page can add labels to it. Any existing labels appear at the bottom-right of the page, below the page content.

...