In this case, Enterprise Keywords.
Go into Document Library settings and switch them on in there.
Edit the view in the library to include the column called Enterprise Keywords.
Users can now enter their own values based on the content, over and above the formal metadata structure. This allows people to get more engaged in their content and improve the findability of it.
The keywords are stored centrally in SharePoint and become resuable as more people type them in.
Manage them in the SharePoint Admin Centre in the Term Store.
HOT TIP
Educate people on how to add keywords that describe the content correctly.
