A Hypervelocity Star is a star moving much faster than its neighbors, i.e., whose velocity stands out from the distribution of velocities of its neighbors. A typical star's velocity is 100 km/s whereas a hypervelocity star may have a velocity of 1000 km/s or more, perhaps even beyond the escape velocity of the galaxy. Many are thought to come from the Galactic Center, but some may be from outside the Galaxy.
The first hypervelocity star was identified in 2005. On the order of 30 have been identified and the Milky Way is presumed to have on the order of 1000. The nearest known example (HVS2) is about 19 kpc from the Sun.