(velocity with respect to local rest)
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. For distant galaxies, e.g., in
cosmology studies, "rest" might be taken as the motion respect to the
velocity determined by Hubble's law, i.e., per Hubble constant.
Local Group (LG)
radial velocity (RV)
Sunyaev-Zel'dovich effect (SZ effect)