ITIL® and other service management frameworks refer to "service level agreements" or "SLAs" as the contracts between the service provider and its customers.
Of course such contracts make a lot of sense - but in our view calling them "service level agreements" is not ideal, because such contracts typically need to address lots of other issues in addition to service levels - such as the functionality being offered by the service.
This is why in YaSM we prefer the term "customer service agreement". With this title, it is clear that the agreement covers all aspects of a service which need to be agreed upon between the customer and the service provider.
What is more, we also introduced "service definitions". These are the documents where YaSM defines all properties of a service in detail. The service definitions can be attached to the service agreements - which is a neat way of organizing documents if there are several customers using the same service: In this case, you may have individual service agreements with the clients' contact information etc., and you can simply attach the same service definition to every agreement.
So the familiar concept of service level agreements or SLAs that you know from other service management frameworks is very much part of YaSM, but we prefer the terms "customer service agreement" and "service definition".
Stefan (YaSM community moderator)