The name accumulation/distribution comes from the idea that during accumulation buyers are in control and the price will be bid up through the day, or will make a recovery if sold down, in either case more often finishing near the day's high than the low. The opposite applies during distribution.
N.B. A Chaikin oscillator is formed by subtracting a 10-day exponential moving average from a 3-day exponential moving average of the accumulation/distribution index.