The ATR indicator moves up and down when the moves in the prices become larger or smaller. Traders use the indicator to enter and exit trades and also to put a stop loss in order to reduce the loss if the prices move in the opposite direction. ATR is open to interpretation.
In technical analysis, an indicator called the Average True Range -ATR- can be used as a gauge for historical volatility. Although it is considered as a lagging indicator, it gives some insights as to where volatility is now and where has it been last period (day, week, month, etc.).