HTM and HTML denote file extensions of HTML files. They are files of plain text type. HTML stands for Hypertext Text Type. HTML stands for Hyper Text Mark-up Language. HTML uses mark-up tags for describing web pages. If you use HTML files to build your web page, then a .html or.htm will most likely show at the end of its URL. HTM is used only as an alternative extension to HTML, and this happens sometimes. In certain operating systems, like the Disk Operating System, or DOS and Windows 3.x, they do not permit the use of four-letter extensions.
This means as a substitute of .html they use .htm. As well as in the realm of Windows, three-letter extensions are most commonly used, such as .doc and .exe, and .htm is more appropriate here .htm was used back in the old days, like when DOS was widespread. In the present-day time, computers can now easily support big files and wide length file names. Having a four-letter extension is no longer an issue.