Explanation/Reference:
A Template is used to create a Page and defines which components can be used within the selected scope. A template is a hierarchy of nodes that has the same structure as the page to be created, but without any actual content.
Each Template will present you with a selection of components available for use.
Templates are built up of Components;
Components use, and allow access to, Widgets and these are used to render the Content.
References: https://docs.adobe.com/docs/en/aem/6-0/develop/the-basics/templates.html