TCP stands for Transmission Control Protocol.
TCP is used to send and receive a stream of data on a pre-established
connection. The TCP protocol itself takes care of setting up the
connection, and ensuring that all transmitted data is received correctly.
TCP is more reliable than UDP,
but is more complex to use and requires
more RAM. The additional RAM usage comes from, in part, the necessity to
retain packets that have already been sent onto the network until they
have been correctly acknowledged (in case the packets need to be
retransmitted), and the need to assemble data that is split between
multiple packets into a reliable stream.