Bar graphs (charts) are a type of graph that are used to display and compare the number, frequency or other measure for different discrete categories of data.
The x-axis represents the different categories and so has no scale. In order to emphasise the fact that the categories are discrete, a gap is left between the bars on the x-axis. The y-axis does have a scale and this indicates the units of measurement.
Mrs. Hall asked her students what kind of pet they have.
How many students have a pet bird? 2 students have a pet bird.