IfcPropertyTemplateDefinition is a generalization of all property and property set templates. Templates define the collection, types, names, applicable measure types and units of individual properties used in a project. The property template definition can be: 

• Property set template - IfcPropertySetTemplate, a collection of property templates that determine the definition of properties used within a project context.
• Property template - IfcPropertyTemplate, a single template that determines the definition of a particular property used in the same project context. The template may determine the name, description, data type, the unit, or a standard expression for each property that is based on that template.