The Free On-line Dictionary of Computing (18 March 2015):
(Or connection-based, stream-oriented). A type of
transport layer data communication service that allows a host
to send data in a continuous stream to another host. The
transport service will guarantee that all data will be delivered
to the other end in the same order as sent and without
duplication. Communication proceeds through three well-defined
phases: connection establishment, data transfer, connection
release. The most common example is Transmission Control
Protocol (TCP), another is ATM.
The network nodes at either end needs to inform all intermediate
nodes about their service requirements and traffic parameters in
order to establish communication.
Opposite of connectionless, datagram. See also circuit
switching, packet switching, virtual circuit.