(TCP) The most common transport layer protocol used on Ethernet and the Internet. It was developed by DARPA.
TCP is the connection-oriented protocol built on top of Internet Protocol (IP) and is nearly always seen in the combination TCP/IP (TCP over IP). It adds reliable communication and flow-control and provides full-duplex, process-to-process connections.
TCP is defined in STD 7 and RFC 793.
User Datagram Protocol is the other, connectionless, protocol that runs on top of IP.