QUESTION: What is the definition of the term "galaxy?"

ANSWER from Meenakshi Sahu on March 25, 1996

A galaxy is an entire system of stars. Our Sun is located in a stellar system
called the Milky Way. From long exposure images made with large ground based
and space telescopes, we know today that the Milky Way is similar to countless
other galaxies and we now recognize that galaxies are the major structural 
units of the Universe.

On a clear, dark night we can see, in addition to the brightest stars
(which are fairly uniformly distributed on the sky) a faint band of light,
cut by a dark rift, stretching around the sky. This faint glow is the
whole impression produced visually by our Galaxy, the Milky Way and the dark
band is caused by obscuring dust, which sverely limits our ability to see
distant parts of the system. Galileo (in 1610) turned his telescope to the 
Milky Way and discovered that it could be resolved into countless
faint stars. It was then realized that the Milky Way could no longer be
attributed to some "luminous celestial fluid" but instead originated 
from vast numbers of unresolved stars or in other words, the Milky Way was
discovered to be a stellar system.