Att can mean attributes or attack. Def is defence, like Dio said. And same with everything else.
If you want what each means per se....
Attack - How much damage they can hit.
Defence - Factors in reducing total damage received.
Spirit - I'm guessing it's a replacement for int stat, so it'd probably affect magic abilities.
Agility - Speed, determines who goes first in turn based games. Plays a major role in evading attacks.
Resistance - Strengths/weaknesses against elements and/or status ailments
Dex - Accuracy, how often they hit. It also plays a minor role in evading attacks.