This model provides a precise measurement of computing power and a consistent licensing metric, regardless of whether your BTS solution is deployed across servers on-premises, virtually or physically, or cloud environments under License Mobility with Software Assurance. The number of core licenses needed depends on whether you are licensing the physical server or individual virtual operating system environments OSEs. BizTalk Server is licensed exclusively in the Per Core licensing model. Per Core licensing provides customers with a precise measure of computing power and a consistent licensing metric, regardless of whether solutions are deployed on physical servers on-premises, or in virtual or cloud environments. Under the Per Core licensing model, each server running BizTalk Server software must be assigned an appropriate number of BizTalk Server core licenses.
An Application must represent a significant functional and value enhancement to the Software such that the primary reason for a Customer to license the Application is other than the right to receive a license to the Software included in the Application. Non-Production environments include development and test environments. Only Licensor and or its authorized representatives are permitted to produce Product Keys for Software. Production environments include quality assurance, disaster recovery, failover, and high availability environments. If and to the extent the relevant Order Form covers Software, then the terms and conditions of Attachment 1 to this Agreement shall govern Customer's access to and use of that Software. If and to the extent the relevant Order Form covers Cloud Services, then the terms and conditions of Attachment 2 to this Agreement shall govern Customer's access to and use of the Cloud Services.
Source for pricing: You have to have that document to see the side by side comparison grid of the different versions of BizTalk Branch, Standard, Enterprise, and Developer. The biztalk licensing difference between Standard and Enterprise, as it has been or many years, is that the Standard edition is limited to 8 biztalk licensing, and it only allows 5 applications. What is an application?
Explaining System Center 2012 Licensing