moodle/lang/en/help/courseshortname.html

<p align="center"><b>Course short name</b></p>

<p>Many institutions have a shorthand way of referring to a course, such as 
   BP102 or COMMS.  Even you don't already have such a name for your course, 
   make one up here.  It will be used in several places where the long name 
   isn't appropriate (such us in the subject line of email).</p>