high-velocity cloud

A high-velocity cloud is a gas cloud within a galactic halo moving at a high velocity, e.g., local standard of rest velocities in or beyond the 70-90 km/s range and with masses ranging up to millions of solar masses. They're largely observed within the Milky Way (such as the Magellanic Stream and the Smith Cloud) and in other nearby galaxies.

The term intermediate-velocity cloud (IVC) is also used for similar clouds with significant motion but somewhat lower velocity. LVC, for low-velocity cloud, generally meaning no more than 35 km/s.