From a practical perspective the
easiest way to understand noise
is to see it,where more noise
equals increasing graininess and
random flecks of colour.
this hyperlink
http://www.neatimage.com/examples.html
illustrates the difference between
noise in the original photo and one
which has had the noise filtered out.
This hyperlink
http://www.dpreview.com/learn/?/Glossary/
Digital_Imaging/Noise_01.htm
explains in more detail and shows
an enlargement of blue sky and the
amount of noise from 4 different
classes of camera(where D is the worst)and one shot of noise reduction.
This hyperlink
http://www.dpreview.com/reviews/panasonicfx01/page6.asp
shows the effect of increasing noise as the camera sensitivity
is increased from ISO 80 to ISO 1600 between 2 diffrent cameras
on a test shot of 1/3 grey,1/3 black and 1/3 detail(queen).
This last hyperlink is a good
photo explanation of noise in
a technical sense.
http://www.cambridgeincolour.com/tutorials/noise2.htm
I would strongly advise Missy to
research noise on the camera she
is intrested in as it can be
particularly annoying when viewing
photos(taken with a compact digital)on a large screen.
Reviews on http://www.dpreview.com/
or http://www.dcresource.com/ will
usually show test shots of the amount of noise on
the camera they are reviewing
(Thanks Barney. -Paul Zucker)