The symmetrical triangle, which can also be referred to as a coil, usually forms during a trend as a continuation pattern. The pattern contains at least two lower highs and two higher lows. When these points are connected, the lines converge as they are extended and the symmetrical triangle takes shape. You could also think of it as a contracting , wide at the beginning and narrowing over time.
While there are instances when symmetrical triangles mark important trend reversals, they more often mark a continuation of the current trend. Regardless of the nature of the pattern, continuation or reversal, the direction of the next major move can only be determined after a valid breakout.
For a break to be considered valid, it should be on a closing basis. Some traders apply a price (3% break) or time (sustained for 3 days) filter to confirm validity. The breakout should occur with an expansion in volume, especially on upside breakouts.