Hi @ramallafre,
Property Set Definitions and Property Definitions are the things that you create in the Style Manager. A Property Set Definition contains Property Definitions. They don’t contain any actual values, but rather the definition for the properties when they get assigned to objects.
Once a Property Set Definition and Property Definition have actually been applied to a specific object, then they are Property Sets and Properties, respectively.
There are a couple of nodes in the Civil 3D Toolkit that you might take a look at as well.
