The slant height is used to find the total surface area of a pyramid. The slant height is not the height of the pyramid. This video describes how to find the slant height of a pyramid.
Question answered in this video
What is a pyramid?
What is the lateral side of a pyramid?
What is the apex of a pyramid?
How is slant height different than the height of a pyramid?
How can you use the 30-60-90 rule to find the slant height?
How do can one use the Pythagorean theorem to find slant height?