TCP half-open
TCP connections are referred to as half-open when the station at one end of the TCP connection has crashed, or otherwise removed the socket without formally notifying the other end of the TCP connection.
Due to the stateless nature of the Transmission Control Protocol, it is possible that if the end of the connection on which the socket still exists is not expecting a response, then the socket may persist indefinitely in this state, known as half-open.
Note: A common misconception is that the term TCP half-open applies to an partially completed TCP handshake state. A better term for this state is an embryonic state.