What is Web services in simple terms

Question

I am little bit confused about what really a web service is. You say Amazone web services,etc like that, they offer information. So what is the requirement to be a web url to be

Answer 1

The W3C defines a Web Service as (quoting) :

A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP-messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.

That definition is maybe a bit too restrictive, considering how that term is used nowadays -- I'd probably go with just the first part of that definition, which is quite generalist :

A Web service is a software system designed to support interoperable machine-to-machine interaction over a network.

Wikipedia also has some interesting definitions, like :

In common usage the term refers to clients and servers that communicate over the Hypertext Transfer Protocol (HTTP) protocol used on the Web.

From what I've seen :

• A couple of years ago, when we said "web service", we generally meant "SOAP, WSDL, ..."
• Now, when we say "web service", we often mean "whatever allows to call something on another server, be it SOAP, REST, ..."