App vs Software

Why do people call mobile applications "apps" and not say that it's just software. This is a good question and here goes the logic answer and I hope you can get this.

A software refers to a set of programs, procedures, algorithms and it's documentation concerned with the operation of a data processing system. It's data that is stored on your phone or computer. ex. Microsoft, Android, iOS, etc.
You can update your system software which is already located on your device, but you cannot run it.

Whereas, an application or application software used to run and perform various tasks.

That's the difference and that's why it's two different things. One software runs, and the other doesn't.