Transmission Control Protocol. Together with IP, the TCP is the most important protocol of TCP/IP.
The TCP protocol creates an higher level abstraction of a reliable stream of data between two hosts on top of
IP, that alone is only able to unreliably send packets of data between hosts.
IP packets can get lost, duplicated, transmitted out of order, so TCP users
retransmission algorithms, and sequence numbers, and the TCP window, to provide reliability and the
abstraction of a continuous stream of data from an end to another.
See also: IP, ICMP, UDP.