Cron jobs are the way a Unix system do things on a regular basis.
For instance, lauching a script each night à 01:00 AM for backup purpose,
or cleaning temp directory each week, and so on.
There a table ("cron tabs") which tell to the Unix system what to do and when.
Sure your can do "things" with MySQL with cron jobs (like backup database for instance)
but they are not tied together.