As my understand, XAML is just a kind of XML which is a standard that uses
declaretive XML language to describe application programming including how
it shows the UI, how it repsonses the user action...
WPF is the first engine developed by Microsoft that takes advantage of XAML
language. WPF's implementation is based on XAML. Silverlight concept comes
out from WPF on Web. So we can just consider Silverlight a web version of
WPF engine developed by Microsoft. So, XAML is just some foundation that
WPF and Silverlight lay on. But we cannot say a XAML application must be
WPF or Silverlight. Maybe in future, there may come out some names(those
are concepts about WPF on SmartPhone, WPF on Cloud, WPF on ....) which all
uses the XAML as declaretive programming language. Even, the third party
company may obey XAML standart to develop some kinds of new engines to do
computer programming everywhere.
That is my opinion.
By the way, we are migrating managed newsgroup to Microsoft MSDN forums. So
in future in you have any questions related to dotnet.general, you can try
to post in the C# general, CLR, BCL forums to get a repsonse from our
support. :-) For this specified discussion, I think WPF forum is more
Microsoft Online Community Support