Term used in two main senses with respect to art: generally, for any systematic technique that renders the illusion of recession behind a two-dimensional surface (including receding lines, gradients of colour, tone and texture, degrees of clarity etc); but also more specifically, for the geometrical technique of linear perspective, the modern form of which was invented in the early Renaissance. . . . At its simplest, linear perspective relies on the way in which sets of inclined lines tend to be read as signalling some degree of space behind the surface on which they are drawn.
Janis Callen Bell