Here is a good site that has some very cool infor about XAML. XAML.NET They have a very nicely worded definition on their main page which I will include here. I hope that they don't mind my posting their content directly. I definitely recommend their site for finding good XAML info. i strongly recommend for folks to get up to speed on it since it will have a trememndous impact on our future software development.
What is XAML? (Extensible Application Markup Language; pronounced "zammel")
XAML is a declarative XML-based language that defines objects and their properties in XML. XAML syntax focuses upon defining the UI (user interface) for the Windows Presentation Foundation (WPF) and is therefore separate from the application code behind it.
Although XAML is presently for use on the Windows platform, the WPF/E (Windows Presentation Foundation/Everywhere) initiative will eventually bring XAML to other platforms and devices.
XAML syntax describes objects, properties and their relationships to one another. Generic XAML syntax defines the relationship between objects and children. Properties can be set as attributes or by using 'period notation' to specify the object as a property of its parent.
<child property="x" property="y">
<class property="u" property="v"/>