Each one uses the file extension you want. There is no universal standard.
The most common is .html
. In Windows some people prefer to use .htm
, but it does not change anything.
The .dhtml
can be an extension that indicates dynamic content for them, something that the HTTP server is configured to process differently by calling an application that will interpret that and generate output. It could be that this page is generated by PHP, for example, so instead of putting .php
in the files they put .dhtml
.
The ghtml
must be some other type of page that requires another application to be called to interpret it.
Even .html
may be calling an application to process. Twenty years ago I did this and the webmasters of the time were intrigued how I could make a page "dynamic" as it is a "standard HTML".
That's what I can answer. Exactly what they do only they can respond. There may be other reasons, but I think this is just to indicate which application to call to process page content.