This TCP flag instructs the sending system to transmit all buffered data immediately.

SYN synchronizes sequence numbers to initiate the TCP three-way handshake and has no role in controlling data buffer flushing.

RST abruptly terminates a TCP connection or rejects an invalid incoming segment and is unrelated to buffered data transmission.

The PSH flag signals the sending TCP stack to immediately transmit all data currently held in its send buffer rather than waiting for the buffer to fill. The receiving TCP stack is also directed to push the data to the application layer immediately, which is essential for interactive, low-latency protocols such as Telnet and SSH.

URG marks a segment as containing urgent data and sets the urgent pointer, indicating out-of-band priority data, but does not flush the send buffer.

FIN signals the graceful closure of one half of a TCP connection, indicating no more data will be sent, and does not force transmission of buffered data.