A Stochastic Oscillator in Forex is a momentum indicator used to identify potential trend reversals by comparing a currency pair's closing price to its recent price range over a specified period, typically indicating overbought or oversold conditions when the reading falls above 80 or below 20 respectively, helping traders anticipate potential price corrections; it is represented by two lines, %K (fast line) and %D (slow line), with buy signals often occurring when the %K line crosses above the %D line from below and sell signals when it crosses below the %D line from above.