Trendlines are a variation of Support and Resistance. While Support and Resistance are formed on a horizontal line/price, Trendline supports the price from below, during an Uptrend. If there is a Downtrend prevailing, the Trendline resists the price from above. Simply said, Trendlines are a variation of Support and Resistance, that are formed in a trending market under an upward or downward angle.
Support is a strong trading tool of technical analysis. It is based on a number of bottoms that are formed at the same level. In other words the Lows just refuse to sink even lower.
Rounding Top belongs to the basic chart patterns. Because of its simple shape, it is very easy to identify in the price chart. To form Rounding Top the trend slows down, then stagnates and in the end reverses its direction. By such process an immutable shape of Rounding Top (like Rainbow) is created. The RT predicts a trend reversal - from an Uptrend to a Downtrend.
Head and Shoulders and Inverse Head and Shoulders belong to the very fundamental chart patterns of technical analysis. They both predict trend reversals.
Double Top and Double Bottom belong to the very basic Patterns of Technical analysis. Their main advantage is that these patterns can be identified in the chart very easy and consequently used for our market trading.