The Parabolic SAR indicator is a well-known forex indicator that uses a price and time-based system to identify trends and potential trend reversals. It places dots on a chart as trailing stops to show where the trend may be ending. The SAR will follow and trail the trend as it ranges over time but will stop and reverse if the price breaks through the indicator, indicating a potential reversal in the price movement.

1. Forex Indicators
This Parabolic SAR (Stop and Reverse) is one of the well known forex
indicators which, talks about the price and time based grading system. It
was designed by wilder with a purpose to hold the trend and follow it as a
trailing stop. It is an indicator which is used to define where the trend
ending point is, by placing the points, dots, on a chart, which will indicate
possible reversals in the price movement. SAR will trail the when trend
ranges over time. The indicators in this SAR will stop and reverse when the
price trend reverses and breakdowns beyond or beneath the indicator.
http://www.parabolicsar.org/