Cron jobs

Cron is a daemon which automatically runs scripts/programs in the background at specific intervals of time. crontab is a utility for handling per-user crontab files. crontab -e is the general means of editing them. These files contain entries regarding times and actions. These periodically executed processes are collectively referred to as cron jobs.

There are actually a variety of "crons" such as "Dillon's cron", "Vixie cron", etc.

Note:

if you add a cron job using "%>crontab FILENAME", make sure the file permissions on the FILENAME are strict (that is 600 -> rw for owner and none for group,other)