crontab

Cron is driven by a crontab, a configuration file that specifies shell commands to run periodically on a given schedule. The crontab files are stored where the lists of jobs and other instructions to the cron daemon are kept. Users can have their own individual crontab files and often there is a systemwide crontab file (usually in /etc or a subdirectory of /etc) which only system administrators can edit. Each line of a crontab file represents a job and is composed of a CRON expression, followed by a shell command to execute. Cronjobs and crontab is used to automate execution of certain web scripts or actions on a web server. You can automatically generate files using time as variable. Like sending out a mail every sunday, automatically calling a mail script. Ofcourse you can also use autoresponders or mail services for such a thing but it's just an example