Website, also written as web site, or simply site, is a set of related web pages.
Web application or web app is a client-server software application in which the client (or user interface) runs in a web browser.
Generally sites with contents which are informational and dont have focus on user interactions are websites.
Whereas webapplications require some user interactions and they have programming/scripts with dynamic contents we call them webapps.
For example :
Personal Information Managers
Also there are views that they are no different from one another.
Websites Vs WebApps:
Yes .you can find webapplications in websites
But we have definitions for what a webservice is :
a software system designed to support interoperable machine-to-machine interaction over a network
Consider you create a web application and need the data to be integrated in another device or smartphones using standards like XML, SOAP, WSDL and UDDI.
Those integrated systems are termed as webservices.
These webservices will be invoked by the client system from a url assigned to the webservice ,the output would be data from the webapplication