On hot summer days, city kids will sometimes open a fire hydrant and let the water gush into the street. Things that gush come streaming out.
Water can gush out of a hose or a drinking fountain, and you can also call the jet of water itself a gush. A more figurative way to gush is to talk enthusiastically about something — you might gush when you're describing your favorite teacher. Gush comes from the twelfth century English word gosshien, originally "make noises in the stomach," and later "pour out." Gush is an onomatopoeic word — it sounds like what it means.