A revit family contains the DNA of how to make an element in Revit, and when you author Revit families, you are writing the DNA code for an element. The family describes the basic geometry of the element, the behavior/relationships of the geometry, and defines the element’s parameters.

When you place a family into a model, this DNA is used to make the element. If you need a different size element, the DNA in the family remains consistent and tells your element how to create a different-sized version.