Triangle patterns are well-known chart patterns within the field of technical analysis. They exist in different formations, bullish, bearish or symmetrical.
All triangle patterns have in common that the price moves in an increasingly narrow price channel until the price breaks out of the pattern up or down. Once that happens, the pattern is complete.
Technical investors use these breakouts to take positions. In the case of the ascending and descending triangle formation this is usually in the direction of the previously existing trend, therefore both these patterns are considered continuation patterns.
The symmetrical triangle pattern can be either a continuation pattern or a reversal pattern.
During the formation of the pattern, the volume will typically be lower, the price moves within the boundaries of the pattern. A true breakout from the pattern is characterized by a sudden uptick in trading volume. This is evidence that many traders recognize the pattern and act accordingly.
More detailed information about the various individual triangle formations can be found here:
The ChartMill Team