The Average Directional Index (ADX) is a popular and free Forex indicator used by traders to identify the strength of a trend. The ADX is a great tool for measuring the strength of a trend, as it can help traders identify when a trend is developing, and when it is weakening. The ADX is a versatile indicator that can be used to determine the strength of any trend in the Forex market, allowing traders to make informed decisions on when to enter and exit positions.