Peter, I normally use the designations, treble and bass rather than top and bottom just to eliminate the confusion you noticed. Having said that, I most often see the term top string used to mean the treble string; the one closest to the floor. In the same vein, we talk about moving up the neck of a stringed instrument to reach higher notes when proper posture usually dicates that the higher pitched frets are closer to the floor.

I think my terminology is generally used by most people who post here.

      - Mark