From what I remember it refers to a thrust bump option which was available. I specifically recall the 'Denver Bump' option which was available for aircrft operating out of Denver airport.
I think it was a sort of preset derate option but I'll have to check with Malcolm tonight as he told me he knows everything!
I seem to recall 'bump' switches on the throttles of some of the A320s I've worked on in the past (they had V2500s).
The ones I see now have CFMs and I haven't seen anything about bumps for a few years now.
Pengineer