Here's a breakdown:

* Vertical distance: Elevation measures how high a point is compared to another point.

* Reference level: The most common reference level is mean sea level, which is the average height of the ocean's surface over a long period.

* Mean sea level (MSL): This is a hypothetical surface that represents the average level of the ocean's surface at a specific point in time. It's used as a standard reference point for measuring elevation.

In simpler terms, elevation tells you how high something is above sea level.