FTP is the historically standard protocol for copying files from one computer to another over a network connection (TCP/IP, so any host on today's Internet, but it wasn't always the case). Many people including many developers learned how to use an FTP client on Windows in order to connect to a server and upload and download files.

Stop using FTP!

FTP is not secure for the same reason that HTTP is not secure and why there's a movement (Let's Encrypt) to move every website to use TLS, i.e. HTTPS instead of HTTP. The reason HTTP and FTP are not safe is that they are not...