What is a CRON job?
Cron Jobs help you schedule and run certain tasks on your server. Cron jobs are used to automating tasks that run on the background periodically, e.g. in web applications like LiveAgent. "Cron" is a time-based task or job organizer in operating systems based on Unix (Mac OS, Linux, FreeOSBD etc.). These scheduled jobs or tasks are referred to as "Cron Jobs".There are various circumstances when an online app may need certain task to run habitually. For example, Send emails in bulk or fetch data.
Here is a simple cron job:
*/5 * * * * /usr/bin/php /www/virtual/username/cron.php > /dev/null 2>&1