A histogram is a chart that shows how the values in a data set are spread out. The range of the data is cut into equal intervals, called bins, and a bar is drawn over each bin whose height is the number, or the share, of observations that fall inside it. In markets the usual subject is a series of returns: a histogram of a stock's daily percentage changes gives a quick picture of its probability distribution.
Analysts read the shape for three things: where the bars peak, how wide they spread, and whether one side stretches further than the other. Laid against a normal distribution, a histogram of daily returns typically shows a taller centre and more extreme bars, the signs of kurtosis and fat tails, and often some skewness. The word also names the bar display of the MACD indicator, which plots a difference between two lines and is not a frequency chart.