Stochastic oscillator
The stochastic is a 0 to 100 oscillator that places the close within the high-low range of the last N periods, often 14.
Developed by George Lane, it rests on a simple idea: in an uptrend, closes tend to be near the highs; in a downtrend, near the lows. The %K line measures that position, and the %D line is a moving average of it, often over 3 periods.
The classic thresholds are 80 (overbought) and 20 (oversold). Signals come from %K and %D crossing in those zones, ideally in the direction of the larger trend.
Twitchier than the RSI, it gives more signals, and therefore more false ones. It works better in a range than in a strong trend, where it stays pinned to the extremes.