Files that contain the .htm file extension usually hold HTML web page files. These files are used to format and display images and text in a user's Web browser.
An HTM file contains HTML markup code that is stored in a plain-text format. HTML stands for Hypertext Markup Language. The HTML language allows a website designer to create structured documents by creating headings, paragraphs, lists, bullets, links and quotes using the HTML language.
Files with the .htm extension are just like files with the .html extension. The .htm extension was introduced with the use of certain Web development software applications like Microsoft FrontPage and Expression Web.