Protocol

A protocol is the "language" chosen to communicate between two computers in networks.

Popular protocols include:

HTTP Hypertext Transfer

FTP File Transfer

Telnet Simple Remote Shell

SSH Secure Shell

TCP Transmission Control

UDP Universal Datagram (Raw)

POP3 Post Office (Mailbox)

SMTP Simple Mail Transfer (sendmail)

Jabber open source instant messages

IRC internet relay chat

and others ... (add here)