The presentation Windows AppFabric Overview uses an interesting terminology and division of service clients and services in a general services architecture:

• Front-End Clients
  • Web Browser & RIA (AJAX, Silverlight)
  • WPF & WinForms
  • Mobile Clients
• Middle-Tier Clients
  • ASP.NET Pages
  • Other Services
• Back-End Services
  • WCF SOAP Services
  • WCF Workflow Services

 Some notes on the general services architecture:

• Services provide functionality to front-end and middle-tier clients.
• Front-end clients can request service functionality through the middle-tier clients or directly from the back-end services.
• Back-end services implement entity, task, and utility service models, provide access to data, and expose application logic.
• Example of entity, task, and utility service model: Customer, Invoice Approval, Tax Calculation.
• WCF SOAP services are defined with code and implement entity and utility service models.
• WCF workflow services are visually defined, provide support for long running processes, and implement task service models.
• Services of one implementation type can easily call services of the other type.