Axis Labels are the labels for the Categories and Values on chart axes. So, where do these labels come from? Category axis labels reflect the Category names within your data (typically within the built-in Excel sheet). Values on the other hand are determined by PowerPoint based upon the maximum value in your data — the minimum value is always set to zero. Of course you can change the Minimum and Maximum values if you want.
Learn how to change the axis labels in PowerPoint 2013 for Windows.

