Height Above Ellipsoid (HAE) is a measure of an object's or aircraft's height above a reference ellipsoid, which is a mathematical model of the Earth's shape. The ellipsoid is used as a standard reference surface, and HAE is the vertical distance from this surface to the object or aircraft. HAE is often used in navigation, surveying, and mapping applications, as it provides a more accurate representation of an object's height than other measures, such as height above mean sea level (MSL) or above ground level (AGL). HAE takes into account the Earth's slightly ellipsoidal shape, which can vary depending on the location and the specific ellipsoid model used.