Radial velocities refer to the measurement of the speed at which an astronomical object is moving towards or away from an observer. This can be determined by analyzing the shifts in the spectral lines of the object due to the Doppler effect. Radial velocities are commonly used in astronomy to study the motion of stars, planets, galaxies, and other celestial bodies, and can provide valuable insights into the dynamics and interactions of these objects in the universe. Additionally, radial velocities can also be used to detect exoplanets by observing the gravitational influence they exert on their parent stars.