A cron job is a command, that runs automatically in the background over a predefined period of time and it runs a script within a hosting account. There won't be any limits in regard to what the script can be - PHP, Bash, Perl, etcetera, what it could do, or what exactly your file extension should be. Examples are supplying a regular report with all of the client activity within a given website, creating a regular backup or erasing the files within a particular folder. These tasks as well as almost every other script can be run on intervals chosen by the user - each few minutes, hours or days, and even once per month or once a year according to the specific objective. Working with cron jobs to speed up numerous elements of administrating a website saves lots of time and efforts.