This is one of the six topping and bottoming structures found around every point of reversal on your charts. Double or top or bottom pullbacks essentially the reverse sequence of square roots.

Due to the nature of the sequence, they are much less common.

A double / triple top or bottom is made, then broken. In the case of a square root, the spike completes the pattern.

In the case of a high, a double top is made. On the second push, the new leg makes a new low. Price them pulls back inside the range, and fades.

In the case of a low, a double bottom is made. On the second push, the new leg makes a new high. Price them pulls back inside the range, and fades.

The last point of rejection typically coincides with an area showing multiple rejections through the course of the double top or bottom range.

Like all patterns, these are structural only and best used for navigational reference. Here is a link to an article explaining this.