If you don’t know, there are many flavors of FTP, just like Doritos would have different flavors.
Regular file transfer protocol with no security whatsoever. Port is 21. The data transfer happens on 20.
File transfer protocol using SSL connection. Authentication and data transfer are secured with SSL connection. Port is 990 with data transfer on 989.
Not related to FTP at all. Just a mean of transferring files between network using SSH. Authentication and data transfer are secured with SSH. The protocol used is not FTP. Port is 22.
FTP over SSH (Secure FTP)
Also refers to “Secure FTP”, it’s a combination of SSH and FTP. Authentication is secured with SSH. However, data transfer is not secured, just like regular FTP. Port is 21.
An easy way to remember the differences is to remember that FTPS is using SSL just like HTTPS is. FTPS is the only secure file transfer defined in proposed standard: RFC 4217.
As usual, Wikipedia has it all!