I believe M_Port is specifically a Brocade term.
https://www.cisco.com/c/en/us/products/collateral/storage-networking/mds-9148s-16g-multilayer-fabric-switch/datasheet-c78-731523.html
Intelligent diagnostics/Hardware based slow port detection
Enhance reliability, speed problem resolution, and reduce service costs by using Fibre Channel ping and traceroute to identify exact path and timing of flows, as well as Cisco Switched Port Analyzer (SPAN) and Remote SPAN (RSPAN) and Cisco Fabric Analyzer to capture and analyze network traffic.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/mds9000/sw/5_0/configuration/guides/int/nxos/cli_interfaces/intf.html#69064
SD Port
In SPAN destination port (SD port) mode, an interface functions as a switched port analyzer (SPAN). The SPAN feature is specific to switches in the Cisco MDS 9000 Family. It monitors network traffic that passes though a Fibre Channel interface. This monitoring is done using a standard Fibre Channel analyzer (or a similar switch probe) that is attached to an SD port. SD ports do not receive frames, they only transmit a copy of the source traffic. The SPAN feature is nonintrusive and does not affect switching of network traffic for any SPAN source ports (see the Cisco MDS 9000 Family NX-OS System Management Configuration Guide).
ST Port
In the SPAN tunnel port (ST port) mode, an interface functions as an entry point port in the source switch for the RSPAN Fibre Channel tunnel. The ST port mode and the remote SPAN (RSPAN) feature are specific to switches in the Cisco MDS 9000 Family. When configured in ST port mode, the interface cannot be attached to any device, and thus cannot be used for normal Fibre Channel traffic (see the Cisco MDS 9000 Family NX-OS System Management Configuration Guide).
Kirk...