Hi All,
Let it simplify a bit
2-tier application is the client -server aplication with 
frontend and backend.
At frontend there would be forms, reports which gets filled 
and monitored by backend.

3-tier application has 
presentation layer (browser)
Application layer (code)
Database layer (Database-tables,views,procedures )
web application comes under 3 -tier and window based or 
desktop aplication falls under 2-tier.
Suggestions are welcome