Stands for "Transmission Control Protocol." TCP is a fundamental protocol within the Internet protocol suite — a collection of standards that allow systems to communicate over the Internet. It is categorized as a "transport layer" protocol since it creates and maintains connections between hosts.
TCP compliments the Internet protocol (IP), which defines IP addresses used to identify systems on the Internet. The Internet protocol provides instructions for transferring data while the transmission control protocol creates the connection and manages the delivery of packets from one system to another. The two protocols are commonly grouped together and referred to as TCP/IP.
When data is sent over a TCP connection, the protocol divides it into individually numbered packets or "segments." Each packet includes a header that defines the source and destination and a data section. Since packets can travel over the Internet using multiple routes, they may arrive at the destination in a different order than they were sent. The transmission control protocol reorders the packets in the correct sequence on the receiving end.
TCP also includes error checking, which ensures each packet is delivered as requested. This is different than UDP, which does not check if each packet was successfully transmitted. While the built-in error checking means TCP has more overhead and is therefore slower than UDP, it ensures accurate delivery of data between systems. Therefore TCP is used for transferring most types of data such as webpages and files over the Internet. UDP is ideal for media streaming which does not require all packets to be delivered.