"admin port" is any TCP port open to the router management systems, like Winbox, Webfig, SSH, API etc.
The TCP ports are:
Columns: NAME, PORT, PROTO, ADDRESS, CERTIFICATE, VRF, MAX-SESSIONS
# NAME PORT PROTO ADDRESS CERTIFICATE VRF MAX-SESSIONS
0 ftp 21 tcp main 20
1 ssh 22 tcp main 20
2 telnet 23 tcp main 20
7 www 80 tcp main 20
9 X www-ssl 443 tcp none main 20
13 winbox 8291 tcp main 20
15 api 8728 tcp main 20
16 api-ssl 8729 tcp none main 20```