mostly what others said. it's gonna depend on your hearing it in the way that means the most to you. here are some ways I'd describe it, other than as those have said above:
SOFTEN UP... especially the knees, ankles, elbows, wrists... think of the tires staying on the ground while the bike moves toward your center (your spine), absorbed by flexing at the wrists, ankles, elbows, knees... sometimes you are actually pushing the bike downward to keep it in contact -- as the rocks you hit drive the bike up toward you, you both absorb the upward hit, and then push the bike back down to keep the tires in contact. eventually this translates to a riding style that is more like floating or dancing with the terrain... takes practice, and at first a fairly big amount of focus, but it's within every rider's reach for sure
experiment with how light a grip your hands can use while still keeping good contact with the bike, as this teaches suppleness necessary to the "soften up" concept
if you are a downhill skier, think of the absorption you use when you ski moguls or when you hit a compression
or, think of how you would absorb with your ankles, knees and hips if you were to jump (on your feet, not on your bike) to flat concrete from about 4 feet up...
hope this helps.
PS-- I live in Missoula and am familiar with the rocky trails of Helena, and I know that a "ride soft" strategy is crucial there.
. This also makes sticking to the pedals easier.
