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.