Whatever is grasped by mental designation is the imaginary nature. Non-entities and the appearances of objects arising in the mind are imaginary. The relationship between name and object, such as grasping the name as the object, or mistaking the object as the name, are also imaginary. Outer, inner, fringe and center; big and small; good and bad; space and time, and so on — whatever is grasped by thought is imaginary in nature.
— Jetsun Taranatha