API stands for Application Program Interface. Its goal is to provide an interface so that other programs can send commands that will trigger some process inside the application, possibly returning some output. The concept might seem a bit abstract, but in fact, there are APIs virtually in everything which is somehow related to computers. Let's see some real life examples:
Operating systems or OS, like Windows or Linux, are the programs that allow you to use computers. When you use any application from your computer, it most probably needs to talk to the OS in one way or another, for example by requesting a certain file, sending some audio to the speakers, and so on. All these interactions between the application and the OS are possible thanks to the APIs that the OS provides. In this way, the application need not interact with the hardware straight away, which is a very tiring task.
To interact with the user, a mobile application provides a GUI. The interface captures all...