jet: A long, narrow stream of
material moving at high velocity. Jets
flow from a variety of astronomical
objects, including forming stars,
certain types of nebulae, and some
very energetic galaxies. Jets can
extend many millions of kilometers
and are among the most spectacular
sights in the universe. Jets seen
primarily at radio wavelengths are
called radio jets and may be
responsible for the large radio lobes
observed in radio galaxies and other
strong radio sources.