Each element you place in a drawing is an instance of a family type. Elements have 2 sets of properties that control their appearance and behavior: type properties and instance properties.
Video: Working With Parameters
Type Properties
The same set of type properties is common to all elements in a family, and each property has the same value for all instances of a particular family type.
For example, all elements that belong to the Desk family have a Width property, but its value varies according to family type. Thus every instance of the 60 x 30-inch family type (1525 x 762 mm) within the Desk family has a Width value of 60 inches (1525 mm), while every instance of the 72 x 36-inch family type (1830 x 915 mm) has a Width value of 72 inches (1830 mm).
Changing the value of a type property affects all current and future instances of that family type.
Instance Properties
A common set of instance properties also applies to all elements that belong to a particular family type, but the values of these properties may vary according to the location of an element in a building or project.
For example, the dimensions of a window are type properties, while its elevation from the level is an instance property. Similarly, cross-sectional dimensions of a beam are type properties, while beam length is an instance property.
Changing the value of an instance property affects only the elements in your selection set, or the element that you are about to place. For example, if you select a beam, and change one of its instance property values on the Properties palette, only that beam is affected. If you select a tool for placing beams, and change one of its instance property values, the new value applies to all beams you place with that tool.