PS - What does -ksh mean?

[Bryan Moore]

Here is an example of output from a 'ps'


   PID    TTY  TIME CMD
  8571 pts/28  0:02 cu -s2400 -d 16498696585041 
 19592 pts/28  4:01 cu -s2400 -d 16498696585041 
 24426 pts/28  0:00 /bin/ksh 
 28128 pts/28  0:01 -sh 
 38877 pts/28  0:00 -ksh 
 39030 pts/28  0:00 ps 


What does the - sign mean in front of sh and ksh?

Thanks!

BRYAN R. MOORE          	    |   "Last night I had that same old dream
EMAIL: moore at uvm-gen.uvm.edu	    |    it rocked me in my sleep, it gave me
USMAIL: 12 Waybury Rd. Colchester,  |    the impression the sandman plays for 
  Vermont 05446                     |    keeps..."   Larry Norman