For additional meanings of "Galaxy", please see Galaxy.
A depiction of the Milky Way Galaxy as seen in the astrometrics lab aboard USS Voyager
A galaxy is a dense grouping of stars, held together by powerful gravitational attraction. Because of the extreme distance between galaxies, most of the lifeforms known to science are in our home galaxy, the Milky Way. There have been limited contacts with objects, forces and life from outside this galaxy, however.