A histogram is a type of visualization commonly used to represent the distribution of quantitative data. It is essentially a bar graph-like representation of data, with the x-axis typically representing a range of classes into columns across a horizontal plane. Along the vertical y-axis, the number count or percentage of occurrences of the classes are represented in the data.

Histograms can be used to detect and identify certain patterns in the data, such as ability to measure the center and spread of the data. It can help to identify the average, minimum and maximum values, as well as finding any outliers or peculiarities in the data.

In trading, the MACD histogram is used by technical analysts to indicate changes in momentum. It employs a specific calculation of the MACD, which plots the difference between two time series that represents different moving averages of the market prices. The MACD histogram looks at the rate of move in the MACD and creates a column chart, which gives earlier buy and sell signals than the accompanying MACD and signal lines. It can show changes in the direction, strength and duration of the move, indicating when buyers and seller balance out.

Histograms are versatile tools, providing an easy and efficient way for visualizing data distributions. Their importance lies in the potential to quickly detect areas of potential importance, providing essential visual aids to better comprehend the data. It has become increasingly popular in trading due to its capacity to provide rapid insight into large amounts of data.