A rocket launch is described in terms of the rocket's position with respect to Earth as a whole. Here, Earth is serving as the:

1. To describe motion, you must state position relative to something else that is fixed or moving with known speed and direction. 2. The text gives exactly this case: "a rocket launch would be described in terms of the position of the rocket with respect to Earth as a whole." 3. That background object (Earth) against which position is measured is the reference frame. 4. So Earth here is functioning as the reference frame, not merely an origin point or a vector quantity. _Source: OpenStax Physics Ch 2 "Motion in One Dimension", p.56 §2.1 Relative Motion, Distance, and Displacement_