Basically it's a antioxidant, that comes in capsule form. There seem to be two types to take, "ubiquinol" and "ubiquinone"
Our bodies naturally produce this, but only up to a certain age. (approx 25)
This description puts it much better than how I described it.
"CoQ10 by itself is also known as ubiquinone. To benefit from the form of the nutrient needed to produce cellular energy and help you reduce the typical signs of aging, your body must convert the ubiquinone to ubiquinol."
I pasted that from a website, after doing a search.
I still don't know what it ACTUALLY is though.