What is Message Type? How it is used in BizTalk ?

Message Type is a Context property which   is write  by receive adapter and receive pipeline. You can access this property  inside the orchestration through BTS. MessageType.

In Other words, Message Type  is   a Biztalk System  Property that is promoted  inside by a pipeline and  adapter. It is made  up of Document Namespace and Root Node Name.

Namespace#RootNodeName.

If schema does not contain   any  namespace then Message Type  should  be #RootNodeName.