A hidden line is a line that cannot be seen.

In 3D computer graphics, hidden surface determination (also known as hidden surface removal (HSR), occlusion culling (OC) or visible surface determination (VSD)) is the process used to determine which surfaces and parts of surfaces are not visible from a certain viewpoint. A hidden surface determination algorithm is a solution to the visibility problem, which was one of the first major problems in the field of 3D computer graphics. The process of hidden surface determination is sometimes called hiding, and such an algorithm is sometimes called a hider. The analogue for line rendering is hidden line removal. Hidden surface determination is necessary to render an image correctly, so that one cannot look through walls in virtual reality.

Hidden surface refers to parts of a 3D object that are not visible because they are obstructed by other objects in the scene. Hidden removal is the process of identifying and removing these hidden surfaces from the view to create a more accurate and realistic representation of the scene. This is important in computer graphics to ensure that only visible surfaces are rendered to the viewer.

The hidden line is drawn, however, the edges of the center line can still be seen ( the center line ends up appearing as extra long dashes on either side of the end of the hidden line)

it is a line that is not visible but it is there it is like air