"Oh, meant to say . . ." (2,3,3)
I believe the answer is:
by the way
(Other definitions for by the way that I've seen before include "At the side of the path?" , "Incidentally, as a rather irrelevant comment" , "At the roadside - incidentally" , "Where 14's [HARD SHOULDER] situated" , "In passing, while we're on the subject" .)