A trendline breakout occurs when price decisively moves above a downward (falling) trendline or below an upward (rising) trendline, signaling a possible change in trend or start of a new momentum phase. It shows that the force which was controlling price earlier—either sellers in a downtrend or buyers in an uptrend—is weakening, and the opposite side is gaining strength. A valid breakout is usually supported by strong candles, increased volume, or follow-through price action, and often leads to faster moves in the direction of the breakout, especially when followed by a successful retest of the broken trendline.