PBL, many thanks for that summary of this thread, captures the discussion very effectively. I wish more people provided such overviews, especially on those 20+ pages rumour threads.
But I am even more grateful for the reference you provided.
It's a big help. And it's the definition that works best for most applications I think. (The context that provoked this question is the GPS reported velocity accuracy.)
Genghis, BOAC, Wizofoz, Pugilistic Animus and others with thoughtful contributions to this thread, thank you as well.
ATCast