As a 3D environment, we have 3 axis. X,Y, Z. Y is always vertical on screen. There are actually 2 families kind of projections : symmetric and asymmetric parallel projections.
====Asymmetric :====
X and Z axis form different angles with Y axis.
*'''"Horizontal" Oblique/Trimetric projection :''' [[Pac-Mania]] obviously, yet "Beat Them Up" games (like Double dragon or Renegade) or even few "Shoot them Up"s (Mag Max) do use some kind of this.
**In those case, we can talk about '''Cavalier perspective (E) / Perspective Cavalière (F) / Kavalierperspektive (D) / Perspectiva caballera (E)''' (is there en English equivalent) which is a perspective with unchanged 2D vertical and horizontal and a 3rd Axis in oblique. This specific projection enable to keep the 2D gameplay based on vertical and horizontal movementof sprites on screen.
**As told, the scale of each axis can vary greatly, hence exact actual terms can vary.
*In rare case, the X axis is not "horizontal " on screen(no 90° angle with Y axis).
**as seen in Crystal castles (US Gold)
====Symmetric :====
The X and Z axis form an equal same angle with Y axis
*'''Isometric projection :''' [[Head Over Heels]] is the most well known. it may not be real isometric because it is quite difficult to get the Y axis on the right scale, and those are probably more Bimetric projection actually close to isometric.
*4x1 is better for vertically limited display.
==Masked Sprites and Elements==