Difference between "Onset" And "coming up"

hey guys i just had a quick question about The onset and the come up of a drug, i was reading about mdma on erowid and it says the onset is 20-90m and the "coming up" is 5-20m. Can someone tell me what the difference between these 2 are, aren't they the exact same thing?

Onset refers to the time it takes before you feel any effects. Once you start feeling effects, you are then "coming up"

^^^then once your eyes are wobbling and you writhing your peaking lol.^^^