Revit Architecture classifies elements by categories, families, types, and instances.
Category: A category is a group of elements that you use to model or document a building design. For example, categories of model elements include walls and beams. Categories of annotation elements include tags and text notes.
Family: Families are classes of elements in a category. A family groups elements with a common set of parameters (properties), identical use, and similar graphical representation. Different elements in a family may have different values for some or all properties, but the set of properties—their names and meaning—is the same. For example, six-panel colonial doors could be considered one family, although the doors that compose the family come in different sizes and materials. Structural members (such as w shapes) are another family. See .
Type: Each family can have different types. A type can be a specific size of a family, such as a 30” X 42”(A0) title block or a 32" x 84" (910 x 2110) door. A type can also be a style, such as default aligned or default angular style for dimensions. A family can have several types. For example, a table may be available in several sizes. Each size table is a different type within the same family.
Instance: Instances are the actual items (individual elements) that are placed in the project and have specific locations in the building (model instances) or on a drawing sheet (annotation instances). Each instance belongs to a family and, within that family, a particular type.