What is an FTP account
File Transfer Protocol (FTP) is a standard network protocol used to exchange and manipulate files over a TCP/IP based network, such as the Internet. In other words, FTP offers a convenient and fast way for uploading or downloading files to and from the server. In order to establish an FTP connection you need to have an FTP account on the server. For more information you can read the article "How to connect via FTP and upload/download files".
The FTP account is basically a set of a username and a password that authorizes access to the server via FTP. The default FTP account that is created when your hosting account is set up provides access to the main /www/ folder of your web hosting account. You also have the option to create new FTP accounts and you can do that via the FTP Manager section of your Web Hosting Control Panel (Site Options > FTP Manager).
What is more important is that for each FTP account you can set an access path. This way the newly created account provides access to a certain folder and its sub-folders, while all other folders are inaccessible. That is useful if you wish to provide access to a third party (for example a web designer) to upload to your account without providing full access to that web hosting account.