CLIENT SERVER :In client server application you have two 
different components.Application is loaded on server 
machine while the application exe on every client 
machine.This environment is used in intranet networks.you 
are aware of clients and servers and thier location in test 
scenario.

WEB BASED:It is a bit different and complex application is 
loaded on the server whose location may or may not be known 
and no exe is installed on the client machine.

1. Web applications, sometimes called "thin client" 
solutions, are concerned with performing business tasks 
through a web
interface. Usually, this involves viewing and manipulating 
data in a database. 

2. Client-Server applications, or "Thick Client" solutions, 
are the more traditional way of doing things. The "server" 
side
often has a "middle layer" inbetween the client and the 
database, this is called a "3-tier" solution. Sometimes 
there are
multiple middle layers which interract, and this is called 
an "n-tier" solution. Sometimes there are thin-clients and 
thickclients
interracting with the same back-end systems.