This demo shows two different images taken from the exact same spot. One is distorted. showing the kitchen longer than it really is and the other shows the kitchen as the eye sees it.
Distortion is the transformation of an object and its surrounding area that differs significantly from what the object would look like with a normal focal length, due to the relative scale of nearby and distant features. Wide-angle distortion can be seen in images shot from close up using a wide-angle lens (with an angle of view wider than a normal lens). Objects close to the lens can appear abnormally large relative to more distant objects.
Distortion happens when taking pictures with a wide-angle lens and the photographer is trying to show as much of the house or room as possible. It is often better to take multiple images, versus trying to get everything into one picture.