.htm or .html extension - which one is correct and what is different?

Question

When I save a file with an .htm or .html extension, which one is correct and what is different?

Answer 1

They are completely interchangeable. If I understand the history properly then in the beginning the correct extension was .html but when Windows 95 came along it could only cope with 3 character extensions.

So .html is correct according to some standard or other but in practice it doesn't matter (most of the time...have just done a quick google search and found the following)

There is one area of concern though, most host servers will require your default starting page to be named as "index.html" and not as "index.htm"