Was- Webspehere Applciaion Server, where actually the applcaiton runs in , test or PROD. This is like a heart in any J2ee application.
WSAD-Websphere Stuio Application Developer. As the name indicates, it is where we develop the applciton. you have all the editors for HTML, JSPs, java classes, EJB, XMl etc etc.....It also has a test server built in it. So you can test the applciation, which you are developing.. then finally you deploy the applciton on to real server i.e WAS.