FTP is a program that is used to move files to and from a computer to another computer.
FTP is Fie Transfer Program and is a utility that allows you to efficiently upload or download files from your computer to another computer. To confuse things FTP uses the File Transfer Protocol (FTP) but when people usually talk about FTP they mean the program. The protocol is the rules used by FTP to transfer files.
When you use FTP you open a special connection between your computer and the other that then efficiently transfers the files. People that move a lot of files will use FTP. Most people use a FTP program that is built in the web browser or that is supplied by a hosting site thru their control panel. There re a number of FTP programs available and some are free and some cost. Popular FTP programs include WS-FTP, FTP Commander, Cute FTP and Coffee Cup FTP.
I use FTP to upload and download files for web pages to my webhosting server and also use a specialized FTP program to upload pictures to picture sharing sites.