FTP (File Transfer Protocol) is a common method of moving files between two Internet sites or two computers. FTP is a special way to login to another Internet site for the purposes of retrieving and/or sending files. For instance, if you make changes to your website on your local computer, you would then 'upload' those files to your web server to become viewable on the web. The process your using to move the files between your computer and the web server is FTP. Some TH Media packages allow you to set up multiple FTP accounts. This comes in handy if you have multiple people updating your website. For instance, Tom could update the pages on the site, and Heather could upload the pictures she's taken.
Another example would be the many Internet sites that have established publicly accessible repositories of material that can be obtained using FTP, by logging in using the account name anonymous, thus these sites are called anonymous ftp servers.