The DME's distance measurement is known as slant range; what does this encompass?

The correct answer identifies that slant range refers to the diagonal distance between two points, which includes altitude. In the context of Distance Measuring Equipment (DME), slant range measures the distance from the aircraft to the ground station at an angle, encapsulating both horizontal and vertical (altitude) components. Unlike horizontal distance only, that would ignore the elevation difference, or altitude information on its own, which fails to fully express the nature of the distance observed. This distinction highlights how slant range provides a complete picture of the actual distance in three-dimensional space, incorporating the aircraft's altitude as part of the measurement.