Motion can be defined as a change in the position of a body with respect to time and another body. Motion is relative in physics.
Motion and rest are fundamental ideas in physics. There is no absolute rest as all bodies in the Universe are in a perpetual state of motion. Stars, planets, constellations and even galaxies are in motion with respect to each other.
Planets revolve around stars and galaxies move away from each other. Motion along a straight path is referred to as linear motion. Motion along a curved path is referred to as curvilinear motion.
Motion is measured as the distance covered by an object in a specific interval of time. The units of distance are the Kilometer and the meter. Thus, motion is measured in terms of meters and kilometers.