A classic crappy pseudo-science website 
as below
http://www.paranormalghostsociety.org/dimensionalbeings.htm
or
try this site 
http://mathworld.wolfram.com/Dimension.html
Not all occurrences have to do with ghost or alien beings there are
other paranormal creatures that come from other dimensions, times
and places. They may look hideous, like us, be composed of just the
light. Some may fade in front of you or some may be visible in the
mirror with the proper lighting. Some may not even be aware that
you see them since they possibly exist in another time and space.
Tourist in Sedona see them, people see them in there houses, in the
woods and just about anywhere. This in a way fits into our portals
page and time travel. Perhaps these beings come from another plane
like ours, or another time into the future and they use dimensional
travel since time is different where they exist. They often call
aliens dimensional beings since some UFOs tend to disappear before
our eyes, angels are also higher beings that exist on other planes
in theory that is why they have the ability to watch over you yet
we cannot see or feel them and when seen they are just a being of
bright light. Many hieroglyphs and Petroglyphs found in Native
American caves 30,000 years ago show winged beings entering threw a
portal or holding an object that controls life and death. These
similar hieroglyphs are seen in other cultures such as Egypt? What
does this mean? Simple that beings from portals or vortexes were
often seen, possibly worshiped or depicted around the world 1000s
of years ago. The shadow men are said to be inter-dimensional we
can view there shadow but not there full form usually. After all is
our shadows not 2 dimensional. However you may see these creatures
there are ways to get in touch with them some saying astral
projection is one way or threw meditation and metaphysical means.
We do not have the answers but these are just a few theories. I do
not think dimensional beings are bad even though some look hideous.
Some people who mirror Scry or use Ouija boards are said to see
them. So you see how everything is tying in or connected? We have
to be careful not confuse demons, ghost and dimensional beings with
each other I guess that is the hard part. But occasionally someone
gets one of these creatures on film usually you see them so quickly
and they are gone or fade quickly but yes they do exist and a
sighting can occur fast at any given time.