(Code) templates are a structured description of coding patterns that reoccur in source code. They are typically supported within IDEs to fill in commonly used source patterns.
Code templates are typically used within IDEs (or advanced text editors) in order to automatically generate content on behalf of the user.
A typical use case would be to have the IDE/editor automatically insert various elements when creating a new source code file (for example using a "user provided" copy right header).
Details depend on the underlying tool, example links: