The Binary Application Markup Language is a file format of Microsoft that is generated by compiling XAML files.
Generation
A XAML file can be compiled into a Binary Application Markup Language file having the .BAML extension.), which may be inserted as a resource into a .NET Framework assembly. At run-time, the framework engine extracts the .BAML file from assembly resources, parses it, and creates a corresponding WPF visual tree or workflow. Having this format, the content is faster loadable during runtime.
References
Binary Application Markup Language Wikipedia(Text) CC BY-SA