Stands for Common Gateway Interface. When a web host offers CGI support, it typically means that you can access a folder in your website's root directory (on the web host's server computer) called cgi-bin to which you can upload your own customized scripts or scripts of your choice. These scripts are usually written in Perl and they will add all kinds of sophisticated functionality to your website such as email forms, search boxes and the like.

Free web hosts quite often will offer you ready-made scripts to do the same but will not offer you access to the cgi-bin to upload and run your own scripts. CGI support is standard for commercial web hosting deals. If they don't offer it then find another host (or make sure that you are getting an incredibly cheap deal... actually free is more like it).

Be advised that some web hosts don't always name the folder that contains your scripts cgi-bin. Some hosts will simply call it cgi. Check with your web host's technical support to verify this. Also, to run scripts written in Perl on your web pages, you will need to know the path to Perl. This is typically something like /usr/bin/perl and will be entered as the first line on all your Perl scripts prefixed by the #! characters (hence #!/usr/bin/perl) providing them with the full path to the Perl interpreter on your web server.

Although you can write your own scripts, most webmasters tap into the plethora of ready-made free scripts available out there on the net. To help yourself to some free scripts, visit the NMS Progams page.