In mathematics, altitude is defined as the height of an object, point, or place compared to the sea level. In other words, the vertical length of anything above sea level or from the earth's natural surface is known as altitude.
For Instance, you may hear a lot that an airplane is flying at an altitude of 5000m, or a mountain has an altitude of 200m, which means the distance between the airplane and the sea level is 5000m or the height of a mountain is 2000m.
For a more precise understanding of the concept check out a diagram listed below:
To know more about it, you can use our Altitude (Geometry) Definition.