Read original post at Kraig Brockschmidt's Blog
All of the WinRT collection types are found in the Windows.Foundation.Collections namespace. What you’ll notice immediately upon perusing the namespace is that it actually contains only one concrete class, PropertySet, and is otherwise its chock full of “interfaces” with curious names like IIterable<T>, IMapView<K, V>, and IVectorView<T>.
If you’ve at least fiddled with.NET languages like C# in your development career, you probably already know what the I and <T> business is all about because you get to type it our all the time. For the rest of you, it probably makes you appreciate the simplicity of JavaScript! In any case, let me explain a little more.