RAS refers to the Report Application Server - which is a component of Crystal Enterprise.
It is bundled with CR9, with a COM, Java and .Net based SDK. In CR9 it allows access of reports, via the web in a zero client environment. Via the SDK's, you can integrate report creation, modification and viewing into your application. You no longer need to use the RDC for development and in actual fact, for web or server based applications, RAS is much more flexible. You actually receive a 3 active user license for RAS with CR9.
RAS, as part of the CE installation, will allow you to give your users creation and modification of reports in zero client environment - depending on which license you purchase in CE. There's alot more to it in CE, however, hopefully this gives you enough of an explanation.
cheers...J