A trendline breakout occurs when price moves and closes decisively beyond a well-respected trendline, indicating a possible change in market structure or momentum. In a downtrend, a breakout above the falling trendline suggests that selling pressure is weakening and buyers are gaining control, while in an uptrend, a break below the rising trendline signals potential trend exhaustion. A valid trendline breakout is often supported by strong candle structure, increased volume, and follow-through price action, and traders commonly wait for a retest of the broken trendline for confirmation to reduce the risk of false breakouts.