A world of web, where an organization provide its services like health care, banking, financial etc over the internet to end users.
To grow up business, organizations want to provide their services to more and more end users in simple ways.
So organizations use web app, mobile app, ipad app etc so that one can use their services easily and quickly.
This is where web services comes into picture. Communicating amongst all these entities (web app, mobile app, ipad app etc) without affecting their existence is made possible by web services.