Isometric graphics in video games

In video games and pixel art, "isometric" refers to some form of parallel projection (commonly, the form of dimetric projection with a 2:1 pixel ratio) where the viewpoint is rotated slightly to reveal other facets of the game environment than are typically visible from a top-down perspective or side view, thereby producing a three-dimensional effect. In almost all cases, however, the term "isometric" is misapplied; in true isometric projection, the representations of the x, y and z axes are strictly oriented 120° to each other, whereas in other views the angles may vary. The terms "3/4 perspective", "2.5D" and "pseudo-3D" are also commonly used, though these terms can possess alternative meanings as well.

With the advent of more powerful graphics systems, isometric projection is becoming less common, instead being replaced by perspective projection.

In the fields of computer and video games and pixel art, the technique has become popular because of the ease with which 2D sprite- and tile-based graphics can be made to represent a 3D gaming environment. Because parallelly projected objects do not change size as they move about the game field, there is no need for the computer to scale sprites or do the complex calculations necessary to simulate visual perspective. This allowed older 8-bit and 16-bit game systems (and, more recently, handheld and mobile systems) to portray large 3D areas easily. And, while the depth confusion problems of parallel projection can sometimes be a problem, good game design can alleviate this.

...
Wikipedia