Difference between First or Business (Boing 757)

I am flying SFO-ATL:
DATE: SAT, 29 JUN 2013
FLIGHT: DL 1221
AIRCRAFT: BOEING 757

and then ATL-AUA:
DATE: SUN, 30 JUN 2013
FLIGHT: DL 655
AIRCRAFT: BOEING 757

Both aircraft seem to have the same configuration, yet on has a 'First' class and the other a 'Business Elite'. Why the different names?