2. A(an) of a prism is a perpendicular segment that joins the planes of the bases. (The height h is the length of one.)

A(an)   altitude    of a prism is a perpendicular segment that joins the planes of the bases. (The height h is the length of one.)

Step-by-step explanation:

AN ALTITUDE -  An altitude of a triangle is a line segment that passes through a vertex and is perpendicular to (i.e. forms a right angle with) the base line (the side opposite the vertex). The expanded base of the altitude is the line that contains the opposing side. The foot of the altitude is the point where the extended base meets the altitude. The area of a triangle can be calculated using altitudes: one half of the product of an altitude's length and its base's length equals the triangle's area. As a result, the longest altitude is perpendicular to the triangle's shortest side. Through trigonometric functions, the heights are also connected to the triangle's sides.

Hence , the answer is an altitude .