Files with the SHTM extension are used to store an HTML document together with the SSI (Server Side Includes) code. SSI is a scripting language for embedding server-side code. The SSI code contained in the SHTM file is processed by the server, allowing content to be dynamically added to an existing HTML page. Only after such code is processed by the server and the content is generated, the page is sent to the client's browser.

Files with SSI code instead of the SHTM extension more often use the SHTML extension.