These are lines, both up and down, that are formed by a stock?s price movement. In the simplest sense, trend lines are drawn between a stocks successive lows to find support, and successive highs to find resistance. The more times a stock?s price touches a trendline and holds, the better an indicator it is. Trend lines can be long term and short term, and, as noted, can be used to determine support and resistance. We often use trendlines to help determine when we should enter of exit trades. When we are in positions and following the trend, we do not like to see the stock break its trend for greater than one day. If a stock does that, it has changed its character, and the trendline is most likely no longer in force.