When you save an HTML file, you can use either the .htm or the .html extension. We have used .htm in our examples. It might be a bad habit inherited from the past when some of the commonly used software only allowed three letter extensions.
With newer software we think it will be perfectly safe to use .html.
As a fucking frenchie, I have the unfortunate obligation to answer "the fur pie", fellow frenchies will understand that, again, unfortunate part of our culture.