Anything too small or too large for us to see with our naked eyes. Normal we only see 2-D images, which limits our perception of what they really look like.
My own nature photography would be very cool to see, I think.
I actually just looked up what holograms are. I've heard of them, of course - Tupoc comes to mind as a first point of reference. I saw words like 'physics' and I think my brain shut down at that point. Hehe!
I don't think I like the idea of seeing someone I loved who has passed on as a hologram. Not sure why.
bevo 