The Average Directional Index (ADX) helps traders determine the strength of a trend, not its actual direction. It can be used to find out whether the market is ranging or starting a new trend. Its related to the Directional Movement Index (DMI)
and, in fact, the latter has the ADX line included. The oscillator ranges between 0 and 100 with high readings indicating a strong trend and low readings indicating a weak trend. It is often combined with directional indicators. The indicator was developed by Welles Wilder, who created several core trading indicators.