TCP Maimon scan
This scan technique is very similar to NULL, FIN, and Xmas scan, but the probe used here is FIN/ACK. In most cases, to determine if the port is open or closed, the RST packet should be generated as a response to a probe request. However, in many BSD systems, the port is open if the packet gets dropped in response to a probe.
https://nmap.org/book/scan-methods-maimon-scan.html
How Nmap interprets responses to a Maimon scan probe
Probe Response Assigned State
No response received (even after retransmissions) open|filtered
TCP RST packet closed
ICMP unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) filtered