A stellar stream is a long, narrow association of stars in the Milky Way halo (or halos of similar galaxies). They are interpreted as disrupted satellite galaxies (dwarf galaxies) or globular clusters, pulled apart by tidal forces. The terms tidal arm and tidal stream are also used, generally for such a stream still attached to a discernible dwarf galaxy or globular cluster. Milky Way stellar streams are currently being identified as large-scale surveys of stars (e.g., Gaia) are providing information to determine distances to many stars, so such groupings are evident. Study of stellar streams offers clues useful for refining theories of dark matter and gravity (e.g., modified Newtonian dynamics).