Perspective - Any graphic system used in creating the illusion of three-dimensional images and/or spatial relationships on a two-dimensional surface

Linear or Geometric Perspective - Development of the optical phenomenom of diminishing size by the use of converging parallel lines that meet at a vanishing point

Oblique Projection - Use of 45 degree angles to achieve illusion of deth as opposed to converging parallel lines

Isometric Projection - Achievement of illusion of three dimensionality through the use of 30 degree angles. No side of the image is drawn parallel to the viewer (I.e.) do not align with the eye-level horizon line

Horizon line - line representing the perceived eye-level of the viewer. It can be high, low or centered.