Radial velocity refers to the speed at which an object moves away from or towards a central point. In astronomy, it is used to describe the motion of stars and planets around their respective centers of mass, such as our Sun's movement in relation to other stars in the Milky Way galaxy. The term comes from the Latin word "radius," meaning "spoke" or "ray," which refers to a line extending outward from a central point. In this context, radial velocity measures how far an object is moving along that line of direction away from its center.