Answer 1

Web Application

A web application is a software application that a user runs in the web browser. It have the following features.

It has a User Interface
Runs in Client - Server environment
Client runs it with the help of a web browser
Server process the data based on client request and provide response

Web Service

A web service is an Application Program Interface (API) that runs on the server, which provide data to the client over http through a standardized messaging system. (XML, JSON, etc...). Web services are further classified into SOAP and REST. In the present day scenario most services prefer REST over SOAP.

Example

I'll explain a simple REST call using a GET request to the github api. You can access the details of a github user with the following request

[math]https://api.github.com/users/<user-name> [/math]

See My details in JSON format from GitHub. Click Here And such data can be integrated into a web application, mobile app, etc.

Some other use cases of Web Services are

PayPal api
Facebook api
Twitter api
Conclusion

Both Web Application and Web Service are a kind of same thing, but web application is for the users and Web Service is for Program <==> Program communication.