JIRA is a work scheduling system, it is basically like a giant post-it note, that automatically gives a task a job number, owner, respondant, etc., allowing lots of people access to the database, edit the document as necessary, and create reports on the process.
Within the WMD system, there were two sets of job numbers; one which began with WMD xxxx, which were community found bugs, and JIRA xxxx which were more specific tasks, such as adding menu options, populating career mode events (read contract offers, twitter responses, etc.), tool tips, etc.
If you take a look at the build reports that are listed in the main thread, you'll see what I mean.