When you edit a category or article, autosave creates a backup every 30 seconds.

If you leave without saving your changes, autosave will let you know the next time you come back to the category or article. You'll see a Recover auto-save link just above the editor:

The Recover auto-save link appears just above the editor

Click this link to open a pop-up where you can choose whether to delete or recover that autosave:

Delete or Recover the auto save.

Once you've recovered the autosave, you'll still need to Save the article to permanently save those changes.