Final answer:
The subject of this question is Physics, specifically the concept of frame of reference.
Step-by-step explanation:
In the context of this question, the student is asking about the subject of frame of reference in physics. In physics, a frame of reference is a coordinate system used to describe the position, motion, and other physical quantities of objects. It allows us to determine whether an object is at rest or in motion.
In the given scenario of looking out the window of a moving car, the car itself is chosen as the frame of reference. As the car moves, the houses appear to be moving relative to the car, giving the sense of motion.
This concept of frame of reference is important in understanding relative motion and the observation of objects in different reference frames.