The environment variable 'prompt' is the 'label' at the front of the DOS command line.
prompt $p$g
c:\windows>
prompt Press any key to format C drive
Press any key to format C drive
(This was a popular joke back in the DOS days. Annoying, but basically harmless. No actual format would be done.)
prompt Win4.1 $p$g
Win4.1 c:\windows>
A prompt is any character group indicating the system is ready to accept a DOS command. Some attempts by DOS virii to install 'ANSI bombs' as prompts caused a little consternation back a decade ago, but most of that business is easily prevented with a virus scanning app.