Application software, or app for short, is software that performs specific tasks for an end-user.
Effectively, if the user is interacting directly with a piece of software it is application software. For example, Microsoft Word or Excel are application software, as are common web browsers such as Firefox or Google Chrome.
It also includes the category of mobile apps, including communication apps such as WhatsApp or games such as Candy Crush Saga. There are also app versions of common services such as those providing weather or transport information or apps for customers to interact with companies.
Application software is distinct from system software, which refers to the software that actually keeps the systems running such as the operating system, computational science software, game engines, industrial automation, and software as a service applications.
Instead of interacting with the user, the system software interacts with other software or hardware.
An operating system for example acts as an intermediary between the application software and hardware, controlling input, output and memory allocation, and can schedule tasks for efficient use of the system. Sometimes it may also include accounting software to allocate cost for processor time, mass storage, printing, and other resources.
There is some ambiguity about the distinction between application and system software, since operating systems usually bundle application software.
The distinction is that it is not considered system software if it can be uninstalled without affecting the functioning of other software.
This has caused controversy where a company supplies system software such as an operating system but also produces the application software that runs on it.
The most notable example is with Microsoft, which sells the Windows operating system but also produces the application software such as Microsoft Word. Microsoft was accused of building secret interfaces in the operating system software which would give it an advantage in its application software products.