Scheduling Tasks with Cron Jobs | Nettuts+

“Cron” is a time-based job scheduler in Unix-like operating systems (Linux, FreeBSD, Mac OS etc…). And these jobs or tasks are referred to as “Cron Jobs”.

There is a cron “daemon” that runs on these systems. A daemon is a program that runs in the background all the time, usually initiated by the system. This cron daemon is responsible for launching these cron jobs on schedule.

The schedule resides in a configuration file named “crontab”. That’s where all the tasks and their timers are listed.
(Link: Scheduling Tasks with Cron Jobs | Nettuts+)