An HTML website template is a general-purpose template that can be used in any website (HTML) editor.
Whereas a FrontPage template, by definition, suggests that it can only be used within Microsoft FrontPage, an HTML template can be used in FrontPage - or in Dreamweaver - or in Hotdog - or even in Notepad.
What you are getting when you buy such a template, is basically a website design and a few pages with minimal content. You take that, put in your own content, and add and remove pages as you need to. As you would with any template!
You will take an existing page within the template and copy it to use to create more pages with the same look.
As you build your website, you will need to edit the navigation / menu portion of the template to reflect your own website sections and links.
The beauty of a general-purpose HTML template is that you are not restricted in any way in how you customize it (other than by any terms of use, if applicable) - and you aren't restricted to using a particular HTML editor. When using a FrontPage template, you would change the navigation structure by dragging pages around the FrontPage site navigation window. In Dreamweaver, you are restricted to certain "editable areas" within the template. But if you are editing the HTML of the template itself, you have carte blanche. And you don't have to use an expensive website editor.
HTML website templates overlap with other website / HTML editors. A general HTML template can be edited in FrontPage, for example. Or in Dreamweaver. Or in any editor!
Most template vendors provide HTML website templates. They are not difficult to use, and do not restrict you to one particular (possibly expensive) website editor.