Moderate vibration dampening means the pole absorbs an average amount of the chatter and vibration that travels up from the tip when you plant on hard or choppy snow. It's what you'll typically find in standard aluminum and composite poles without any special shock-absorbing features built in.
For most all-mountain and recreational skiers, moderate dampening hits the sweet spot. You get enough comfort to ski a full day without your hands feeling rattled, but you still maintain a good sense of what's happening underfoot. You might notice some buzz on really firm or icy snow, but it's rarely a dealbreaker.
If you're not dealing with hand fatigue or numbness, and you're not racing at a level where you need maximum snow feedback, moderate dampening is usually the right call. It's the balanced, do-anything option that works for the majority of skiers.