What is the difference between the ACK flag and the RST flag?

The ACK flag validates the receipt of the previous packet in the stream, and the same session is being closed by the RST flag.

The ACK flag validates the next packets to be sent to a destination, and the RST flag is what the RST returns to indicate that the destination is reachable.

The RST flag identifies the connection as reliable and trustworthy within the handshake process, and the ACK flag prepares a response by opening a session between the source and destination.

The RST flag establishes the communication, and the ACK flag cancels spontaneous connections that were not specifically sent to the expecting host.