Transmission Control Protocol (TCP) is a transport layer protocol that provides a connection-oriented data stream service with guaranteed, in-order delivery.
Transmission Control Protocol (TCP) is a transport layer protocol that provides a connection-oriented data stream service with guaranteed, in-order delivery on top of the underlying packet-oriented, unreliable IP layer. TCP is referred to as a connection-oriented protocol. This is opposed to UDP, which offers a relatively bare-bones unreliable all-or-nothing delivery of discrete packets and referred to as a connection-less protocol.
How TCP fits into Internet protocol suite layers (going top to bottom):
- Application: Encrypts data to be sent or sends data in a specific format (e.g. TLS or HTTPS)
- Transport: Splits the data into chunks and adds a TCP header to each (creating a TCP segment)
- Internet: Encapsulates each segment (and splits if necessary) into IP datagram (with source and destination IP address)
- Link: Encapsulates each datagram (and splits if necessary) and adds physical address (MAC)
There is more information at the Wikipedia article on TCP.