Template:Documentation/Doc

is a template used in the the documentation section of other templates.

To reduce system load, Template:Documentation should be employed as part of all high-use templates.

It can be used on any template to simplify the template's appearance in the edit buffer.

It's typically used in the form:

...

The template automatically includes the documentation which is on the subpage "/Doc" of the template. Thus the template proper and the documentation are on separate pages, but the documentation is shown on the main template's page. The separation means that the documentation can be edited without modifying the template itself and without having every page that (in)directly calls the template re-evaluated.