What it is
Before there were indicators, an uptrend meant a series of higher highs and higher lows. Each bar pushes above the high of the bar before it and stays above its low. It is the market saying buyers will pay more than yesterday and sellers will not accept less.
How Breakaway uses it
HH/HL fires when the latest bar's high is above the prior bar's high and its low is above the prior bar's low. It has a short memory, so it flips on and off often. That is on purpose. It tells you the trend is active today rather than in general.
How to read it
On its own it is ordinary. Lit alongside a compression trait and heavy volume, it marks the first bar out of a base. That is the entry many breakout traders wait for. Dark on a stock that is otherwise strong usually means a normal pause. The trade plan's entry above the prior high handles that case. It waits for the next higher high before you are in.