It's a well-known indicator that shows maximal and minimal prices (and average values) of the last n bars.
Translated from Russian by MetaQuotes Software Corp.
Original code: https://www.mql5.com/ru/code/85
The Acceleration/Deceleration Indicator (AC) measures acceleration and deceleration of the current driving force.Average Directional Movement Index (ADX)
The Average Directional Movement Index Indicator (ADX) helps to determine if there is a price trend.