Explain :

An api may be for web-based system, operating system, database system, computer hardware or software libraries.

Api is a Application Programming Interface. Normally everyone use mobile phone and computer applications that are mainly depend on application programming interface.

Everyone download "where is my train" application in your phone that track trains or track bus and aeroplanes. All these work complete by API.

You also can create a train Tracker app if you have official API of indiarail. Indian rail website upload thier Data on thier API amd who use API in app also automatically update.

Easily you everyday see your app, you command on app and api this command to database, and we see results.