My condolences on your loss, Meg.
I have mostly heard of orbs in connection with unexplained light artifacts usually seen on photographs or videos.
The nearest real world reference I can think of would be something akin to a will of the whisp, but those are usually not found in homes and the like.
I am not,myself, someone with a belief in the paranormal or spirit world, and in my opinion it would seem more likely that a more prosaic explanation is at the root of these, but it would be interesting should you see them again.
Our minds, and our vision, are adept at playing tricks on us - after all, what we think of as reality could more accurately be thought of as a mental construct derived from information passed from our sensory apparatus, such as our eyes, and ears, and much of what we see our brain has actually constructed for us.....
http://en.wikipedia.o...normal_interpretation
http://en.wikipedia.o...ki/Will-o%27-the-wisp
http://www.psychic-ex...-story.php?story=6878