Hi Vish,
A web service contains a web method which can be accessed in any where irrespective of platforms. I will give you a real world example. I have developed an app for inkakinada.com in Android. In my Android app, I need some of the inforamation from this site. Here I used webservices, We have created some web services and hosted them in Server, In the Android app we have consumed these webservices to get data..
For more information follow the below links..
http://www.w3schools.com/webservices/ws_intro.asp
http://www.webopedia.com/TERM/W/Web_services.html
Thanks & Regards,
Raghavendra K.
Nyros Tehcnologies