A Swing Low is a valley identified within a series of bars or within an indicator or oscillator. A Swing Low consists of two legs, and starts with an initial down leg which is then followed by an up leg.
A leg is defined as two or more bars going in any one direction. For example, when two or more consecutive bars produce lower (bar) highs and lower (bar) lows. In this instance, the smallest possible down leg would have developed. Inversely, to have an up leg you need no fewer than two bars showing higher (bar) highs and higher (bar) lows. When a down leg is followed by an up leg, the valley that is created is considered a Swing Low.