As the term scheduler can be quite misleading to specific groups of developers, let's clarify the functionalities that APScheduler provides, as well as what it does not provide. First and foremost, the library can be used as a cross-platform scheduler that is also application-specific, as opposed to more common schedulers that are platform-specific, such as the cron daemon (for Linux systems) or the Windows task scheduler.

It is important to note that APScheduler is not, in itself, a scheduling service that has a prebuilt GUI or command-line interface. It is still a Python library that has to be imported and utilized inside existing applications (that is why it is application-specific). However, as you will learn later on, APScheduler comes with numerous functionalities that can be leveraged to build an actual scheduling service.

For example, the ability to schedule jobs (specifically, background ones) is essential for web applications nowadays, as they can include different but important functionalities, such as sending emails or backing up and synchronizing data. In that context, APScheduler is arguably the most common tool to schedule tasks for cloud applications that involve Python instructions, such as Heroku and PythonAnywhere.