peculiar velocity

Peculiar velocity is the motion of an object with respect to local rest. "Rest" depends upon observation and purpose. For a star within a galaxy, "rest" might be taken as the mean motion of nearby stars, i.e., how this star's movement differs from the general motion of those around it. For distant galaxies, e.g., in cosmology studies, "rest" might be taken as the motion respect to the Hubble flow, i.e., the expected motion away from us due to Hubble's law.