Axis is called as a Numeric axis when we Axis represents number scale. In the column chart example below x-axis is a Category Axis and y-axis is a Numeric axis. Its good to know that in a vertical chart x-axis is horizontal where y-axis is vertical axis. And incase of bar chart its just opposite as bar chart is a Horizontal chart.
You need to set x and y property of the DataPoint as number to work with Numeric Axis.

Column chart with category x-axis & numeric y-axis

Bar chart with category x-axis & numeric y-axis

A Chart with both numeric x-axis & y-axis