What does the term "Protocol Heads" exactly mean?

I am currently reading the documentation on Service Bus for Windows Server, and I stumbled over "Protocol Heads". Specifically I am talking about this documentation page: http://msdn.microsoft.com/en-us/library/windowsazure/jj193012(v=azure.10).aspx Unfortunately I could not find a explanation of this term anywhere on the net and not here in this forums. For me there are protocols and protocols can have headers. Thank you.