What is a Cron Job

A Cron Job is a task that should be executed repetitively at regular intervals. It is an action that only your server is capable of scheduling.

Example: the website weekly-backup that most hosting companies offers to their clients, is a classic example of a Cron Job. The server has scheduled the backup operation on, for example, every Saturday night at 00:00.

Crons consist of a server-command that is executed at regular intervals: every day, every month, every Saturday, at midnight, every 10 minutes, every hour etc.. In order to set up such repetitively actions, your server requires a 'Cron Utility' to be installed. One of the most popular Cron Utility for Linux Severs is crontab.

If your server has a Control Panel, then you should check if a feature called 'Cron Jobs' exists. You should ask your hosting company if your server supports any Cron utility to schedule Jobs.
Once you know whether your server supports such functions, you just need to find the command that the server should execute at regular intervals.

Starting from Joomla! 4.1, a new feature has been introduced to create Scheduled Tasks, which are used to run routine site maintenance tasks as an alternative to server cron jobs. Anyway, this is just a workaround, because the registered tasks will be properly executed only if you have some visitors. A server cron job is indeed used to prevent this limitation, as the server periodically invokes itself, just to simulate a user ping/visit.