In TCP/IP networking, the ACK flag is used to acknowledge the receipt of a packet. It's a way to confirm that the previous packets have been received and that the connection is proceeding as expected. The RST flag, on the other hand, is used to reset the connection. It is sent if a segment arrives which is not intended for the current connection, or if a connection request is to be denied. Essentially, the ACK flag is about maintaining the established connection, while the RST flag is about aborting connections that are not valid or are no longer needed123.