Bar charts (also called bar graphs) are very similar to histograms. The only noticeable difference is that the x-axis can represent any kind of categorical data (you can think of it as text values, such as: day of the week, gender, blood type, category name, etc.). The bars on the chart can be arranged in any order and can be plotted vertically or horizontally. The number of bars is usually limited to improve chart readability.
As an example, let's visualize the number of sunny hours for each day of a given week.
The categories (the days of the week) are not numbers, so they cannot be presented with a histogram. However, the bar chart works very well in this case.