What does it mean to see black floating dots in one eye ?

Vitreous floaters: This usually means vitreous floaters which is a benign condition.However ,if you see flashes of light ,this is serious and could mean a retinal tear and you would need to see an ophthalmologist immediately by going to ER for the ophthalmologist on call(NOT for what you are describing).However,you still need to see an ophthalmologist to get a fundus exam which is looking into ur eye with a scope.