The double bottom reversal pattern describes a setup where a stock hits a low twice within a downtrend, each followed by an increase of over 10%, before breaking through a resistance level and confirming it as new support. This signals the potential reversal of the downtrend, allowing traders to initiate a long position with the previous resistance level as the profit target. For a true double bottom, six specific criteria must be met including two bottoms, two increases, a resistance breakdown, and resistance turning to support.