Web application: is a 3 tier arch structure which has a 
client, a server and a database. In the web application, 
core application lies on the server side and client can be 
a thin client like a browser. And what ever changes are 
made they occur at server only and is reflected every where 
else.

C/S application is always a two tier and has a client and a 
server only. In C/S, entire arch is installed at client and 
when ever change is required, all the clients are to 
changed.

WEb applications are 3 tier, no. of users are more, URL 
Driven, session are closed wen u log out , performance 
issues are more related to session time, speed, no. of 
users, security

Client -server are 2 tier with menu driven control, limited 
no. of users, performamce issues are less