What is the difference between 2D, 3D, 4D and „Stereo-3D“ ?

2D representation in 2 dimensions: height and width

3D representation in 3 dimensions: height, width and depth

  Usually „3D“ describes the real three-dimensional representation based on the three-
  dimensional system of coordinates. 
  Especially in the IT-sector for marketing reasons „3D“ is nowadays frequently used for
  representations of objects that are only 2D, but that give a certain three-dimensional
  impression due to projection. This is also called „3D-representation by means of 2D-
  projection“.

4D representation

  Because of the unclear and sometimes false use of the term „3D“ some software-
  and hardware-products did (and some times still do) bear the additional remark „4D“ in order to draw attention that they are NOT takling about a „3D-representation by means of 2D-projektion“ but „more“.

Stereo-3D representation

  Because of the unclear and some times false use of the term “3D” the additional remark
  “stereo” is used to express that there are 2 a slightly different pictures for the right eye
  and the left eye. The remark „stereo“ is chosen according to the audio engineering
  based on two channels that supplies two slightly different acoustic contents for the
  right ear and the left ear.

Supplementary comment to the
Effect of Pulfrich:

To complete the picture some words on a technique that been used some years ago epecially on TV to call attention by the subject “3D”.
Although under certain circumstances it is possible to achieve good tree-dimensional results with this technique, it is not a “Stereo-3D” technique since because it does not use two different pictures for the right eye and the left eye.

The effect of Pulfrich is an optical illusion, based on the fact that a dark optical stimulus is perceived by the brain with some delay in contrast to a light optical stimulus.

The „secret“ of the recording techniques of the effect of Pulfrich is that either the camera or the recorded object (for example a person, an animal, a car etc.) moves steadily in a certain direction.

The „secret“ of the glasses of the effect of Pulfrich is merely that one eye is dimmed. Thus both eyes see the same picture, but the picture of the dimmed eye is perceived by the brain a little later. From this parallax the brain calculates a three-dimensional depth information that is not real at all.
When the movement stops you will only be able to see 2D – even if you are stil wearing the glasses.