Template Files In WordPress
What are we talking about when we speak of templates in the context of WordPress? The short version is that templates are files which tell WordPress how to display different types of content.
The slightly longer version: every time someone sends a request to view part of your website, the WordPress platform will figure out what content they want to see and how that specific part of your website should be rendered.
For the latter, WordPress will attempt to use the most appropriate template file found within your theme. Which one is decided on the basis of a set order, the WordPress template hierarchy. You can see what this looks like in the screenshot below or in this interactive version.