OHLC stands for Open High, Low Close. OHLC charts are helpful because they show the four major data points over a period of time. The chart type is useful because it can show surging or diminishing momentum. Open and close being far apart shows strong momentum, and open and close being close together shows indecision or weak momentum. The high and low show the full price range of the period, helpful in assessing volatility. There are several patterns that traders watch for on OHLC charts.