what is the diffence between WAS and IIS?

WAS is a new feature of IIS, that allows all the features of the Windows Communication Framework stack, like non-HTTP channels and other stuff. IIS is the web server that hosts the services that are activated via WAS.

Check out this document for details.

In case you mean Windows Activation Service: WAS - is the new process activation mechanism that ships with IIS 7.0. WAS builds on the existing IIS 6.0 but is more powerful because it provides support for other protocols besides HTTP, such as TCP and Named Pipes.

The WAS hosting is the real new feature because it provides a concept that extends the ASP.NET HTTP hosting concept (ASMX Web Services). As a standalone Windows component, WAS is completely separated from the IIS hosting environment and provides a protocol-agnostic activation mechanism, so you aren’t limited only to HTTP. WAS allows you to choose the most appropriate protocol for your needs:

• for HTTP, data transfer relies on the ASP.NET HTTP
• for protocols such as TCP and Named Pipes, WAS leverages the extensibility points of ASP.NET for transferring data.

Windows Process Activation Service, also referred to as WPAS, is a new component in IIS 7.0 that manages application pool configuration and worker processes instead of the WWW process. This enables the same configuration for both HTTP and non-HTTP sites to be used.

http://searchwindowsserver.techtarget.com/tip/Windows-Process-Activation-Service-in-IIS-70