- URG — Process the current TCP packet immediately. Directs the receiving system to examine the “urgent pointer” field.
- ACK — Acknowledgement. Directs the receiving system to examine the “acknowledgement number” field.
- PSH — Push. Elevate the priority of the packet’s data, but does not otherwise change rules around packet processing.
- RST — Reset. Terminates the connection forcefully.
- SYN — Synchronize. Used during the initial three-way handshake to set a shared (starting) sequence number.
- FIN — Finish. Indicates that the connection may be dropped gracefully.