A high-velocity star is one moving significantly faster than the vast majority. Typical criteria are 65 km/s or 100 km/s relative to other stars. Some such stars (runaway stars) appear to have been boosted by some event such as a supernova or a stellar encounter involving a binary star. Others appear to be in the higher-velocity portion of large elliptical orbits stretching into the galactic halo, often apparently very old stars. And a few are traveling so fast they appear to near or exceed the Milky Way's escape velocity (hypervelocity star).