Individual is the collection of all things that are not sets or collections. Individuals might be concrete or abstract, and include (among other things) physical objects, events, numbers, relations, and groups. Your car is an individual, but the collection of all four-door sedans is not. This collection (unlike the car itself) is abstract: it doesn’t have a location, mass, or a top speed; but it does have elements, subcollections, and supercollections. The difference between collections and individuals is somewhat like the difference between classes and instances in object-oriented programming.