This is one of the options for displaying the price chart (see) in your terminal. If you open a terminal (see), you will see the top panel above the price chart with three buttons: one will be called "bar graph", another "candlestick" (see), and the third the "line". By clicking the "bar", you clearly see what this same type of graph represents. In fact, the bar is one small vertical line. It gives the trader information about the price changes over a specified period of time. This period, you can choose yourself: for example, you want a detailed timescale and choose the top panel minute time frame (see) M1, or if you want to see what is happening hour by hour H1, and maybe you interested in the global picture, and you select the MN it will open a monthly schedule for you. On this diagram, each bar shows the price change for one month, one after another. Now look at the bar carefully: it contains several parameters that reveal to you the basic information about the behavior of prices in this period. So you can find the "opening price" (the value that was selected at the beginning of the period) and it appears as a small horizontal line to the left of the bar. Next you will find out the "closing price", the last price immediately before the end of the selected period, which appears as a small horizontal line is the right of the bar. The upper point of the bar (vertical line) is the “high”, the maximum value that was reached during the selected time period. So the lower bound, as you've probably realised, is the "low”, the minimum value that was reached during this period.