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

SYN (Synchronize) is used to initiate a TCP three-way handshake and synchronize sequence numbers between hosts, not to flush buffered data.

RST (Reset) abruptly terminates an existing TCP connection or rejects an invalid incoming segment, and has no role in data buffer management.

The PSH (Push) flag instructs the sender's TCP stack to immediately flush its send buffer and transmit the data without waiting for additional data to accumulate. On the receiving end, it signals the TCP layer to deliver the data to the application immediately rather than holding it in the receive buffer. This behavior is essential in interactive protocols like Telnet where low-latency, character-by-character delivery is required.

URG (Urgent) marks specific bytes within the segment as high-priority for out-of-band processing by the application, which is distinct from instructing the system to flush its send buffer.

FIN (Finish) signals the graceful closure of a TCP connection by indicating no more data will be sent, and does not cause immediate flushing of buffered data.