Definitions
1, Lines drawn across successively higher bottoms in uptrending price action or progressively lower tops in downtrending price action. Prices crossing a trendline may indicate a change in direction has occurred.
2, Straight lines drawn on a chart below reaction lows (in an uptrend) or above rally peaks (in a downtrend) that determine the steepness of the current trend. The breaking of a trendline usually signals a trend reversal.