IMO, there's no bright line between the two things.
It's a situational descriptor, in which "bright" is the synonym for the condition of being in the top quartile, but still fitting well enough within the expectations and culture in which one is operating that it feels GOOD, and comfortable.
"Gifted" is a bit of a misnomer, in my estimation, since I tend to think of this term as referring to the situation in which one's differences from the rest of the population cause one DIFFICULTY in terms of "fit." Being out of synch with peers/colleagues, having to choose between one's inner direction and motivations and those which are external (and feel unnatural or even wrong, or overly simplistic)-- that kind of thing.
Among a peer group which ranges from IQ 125-155, persons like my DH and I are going to find ourselves feeling "bright" but not "gifted."
On the other hand, regular day to day life, we are definitely operating as strangers in a strange land, if you see what I mean.
The higher one's LOG (relative to one's surroundings), the more likely the latter seems to be.
