1. Asymmetric drift is the tendency of a population of stars
to have a mean rotation velocity around the galactic center that lags
behind that of the local
standard of rest.
2. Asymmetric drift may also mean the negative of the mean V velocity (one of the components of space velocity) of a stellar population. In general, it increases with random motion within the population, so that the older the population, the more negative the V velocity. For example, the young thin disk population has an asymmetric drift of 0 km/s, whereas the halo population has an asymmetric drift of about 200 km/s.