What does this do: TMyClass(AClass.member).Member?

Hi

I've come across this sort of code:

TUserData = class
public
FRequestCount: Integer;
end;

.......

begin
.... IntToStr(TUserData(AContext.Data).FRequestCount);

Now, AContext is a class and .Data is a property of type TObject. What
exactly is going on here? I don't understand what
TUserData(AContext.Data) is doing. Type casting this some how? or..?
and then the .FRequestCount?

Never come across this sort of thing before.

Thanks, James.

.