TCP, or Transmission Control Protocol, is a communication protocol used for transmitting data over networks. It provides reliable, ordered, and error-checked delivery of data between applications running on networked devices. TCP is responsible for establishing and maintaining the connection between two devices and breaking data into small pieces, or packets, that can be sent and received efficiently. It is one of the core protocols of the Internet Protocol (IP) suite and is essential for many types of computer networking applications, including email, file transfers, and web browsing.