GenerationIP

FTP (File Transfer Protocol) (Port 21) is a network protocol used to transfer data from client to a server FTP through a network, such as over the Internet.

FTP was defined initially in RFC959 and has been updated in RFC2228.

Some data connection is also made from the client to the server ie made to port ftp-data (20).

HTTP  (Hypertext Transfer Protocol) (Port 80) is a network protocol used for the transfer of information on intranets and the World Wide Web. With this protocol you can transfert data or publish some content (HYPERTEXT) .

RFC 2145 describes the use of HTTP version numbers.

Apache, IIS and LightHTTP are HTTP server

POP3 (Post Office Protocol version 3) (PORT 110) is the protocol use by a client application to get email present in the mail server.

POP3 has made earlier versions of the protocol, informally called POP1 and POP2, obsolete. In contemporary usage, the less precise term POP almost always means POP3 in the context of e-mail protocols.

RFC Definition : 

SMTP (Simple Mail Transfer Protocol) (Port 25) is the protocol use to transmit email through a network, such as over the Internet.

SMTP is defined in RFC 821 as amended by RFC 1123. The protocol used today is also known as ESMTP and defined in RFC 2821.