~ Stands for Server Side Includes. This is a method using directives in your HTML code to be processed by the web server in order to dynamically generate certain portions of a web page on the fly before it is sent off to the client browser.SSI is best suited to situations where only small portions of your web page are required to be dynamically generated and is especially useful to insert blocks of HTML code that tend to be repeated across numerous web pages.For instance, Iron Spider contains 150+ pages as of this writing and they all contain the same navigational sidebar menu permitting you to quickly select and jump to another page on this site. Instead of having to rewrite the same menu on all 91 pages every time I add a new page (and thus a new link to the sidebar menu) I create a single Includes file which contains only the HTML code for the sidebar menu which is then saved with the .inc file extension. Then I put the SSI directive on all my web pages which instructs the web server to retrieve the sidebar menu .inc file and automatically insert it on each and every web page. Thus I am only required to update a single Includes file whenever I wish to change the sidebar menu on all 150 pages.To use Server Side Includes, you are normally required to save your HTML files with the .shtml file extension in order to instruct the web server that this file contains SSI directives to be processed. However you can (if permissible) override your web host's server configurations with an .htaccess file to have SSI run on .htm or .html files. SSI can do more than just insert snippets of code into your web pages. To learn about everything you can do with SSI, see Apache Tutorial: Introduction to Server Side Includes. SSI is a standard in basic web hosting packages. If the web host you are considering doesn't support this then move on. You can do better.