FTP or File Transfer Protocol is an internet protocol used to transfer files across the internet from one computer to another.
For example, when you are installing a software like WordPress on your website, then you will most likely use FTP in order to upload all of the WordPress files from your personal computer to your server. In order to do this, you need something called an FTP client. The FTP client is software that runs on your personal computer and allows you to transfer files to and from your web server. Filezilla and WS_FTP are examples of easy to use FTP clients