What does Depth mean?
Correct Answer: B
Rationale: Depth refers to the distance or downward measurement from a surface. It is not the thickness of an object (Choice A), as thickness is the measure of how thick or thin an object is, not necessarily related to depth. Additionally, it is not the length of a surface (Choice C) because length typically refers to the longest dimension of an object rather than its depth. Finally, it is not the area between two points (Choice D) because area is a measure of the space within a boundary defined by points, while depth specifically refers to the vertical distance below a surface.