Distributed Application:

Software that executes on two or more computers in a network. In a client-server environment, distributed applications have two parts: (1) the 'front end' that requires minimal computer resources and runs on the client computer(s), and (2) the 'back end' that requires large amounts of data crunching power and/or specialized hardware, and runs on a suitably equipped server computer.

Web Application:

A web application is an application that is accessed over a network such as the Internet or an intranet.It uses a web browser as a client. The application can be as simple as a message board or a guest sign-in book on a website, or as complex as a word processor or a spreadsheet.