Average Directional Index
An indicator, abbreviated ADX, that measures trend strength on a 0–100 scale without indicating direction. Readings below 20 suggest no trend; above 25 suggest a trend is present.
ADX answers "is there a trend" and never "which way". It is most useful as a filter: trend-following signals mean little when ADX is under 20, because there is no trend for them to follow. It is computed with Wilder's smoothing, which is a running average rather than a simple one.