As it was explained to me OFF is the time frame from when the current med dose begins to loose its effectiveness until the time when the new dose begins to become effective. Sort of like the bottom third of a U My PD is classified as OFF DYSTONIA and for that reason Dr. Fahn suggested Liquid Sinemet to reduce the UUUUUU to uuuuuuuu (smaller waves if you will) It worked fine for about 10 weeks then began to loose its effectiveness. Although the symptoms are the same they seem to last a shorter time and are not as deep. A long answer for a short question Joyce