Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is).
For example, "The height of that building is 50 m" or "The height of an airplane in-flight is about 10,000 m".
When the term is used to describe vertical position (of, e.g., an airplane) from sea level, height is more often called altitude.
Furthermore, if the point is attached to the Earth (e.g., a mountain peak), then altitude (height above sea level) is called elevation.In a two-dimensional Cartesian space, height is measured along the vertical axis (y) between a specific point and another that does not have the same y-value. If both points happen to have the same y-value, then their relative height is zero. In three-dimensional space, height is measured along the vertical z axis, describing a distance from (or "above") the x-y plane.