You can name each axis. This will then be displayed below/next to the axis. For more information, see Showing/hiding axes and axis titles.
Edit properties: To change the properties of the axis title, select it and right-click to open the context menu and choose the command (Category/Value) axis title: Properties.
Tip: Alternatively, you can choose this command via the Edit properties icon 
on the ribbon tab Chart | group Chart elements. The other alternative is to double-click on the axis title.
You can make the following settings:
Format tab
Tip: Borders and fill can also be conveniently adjusted directly via the buttons of the ribbon tab Chart | group Chart elements. For more information, see Editing chart elements.
▪Border section
| Here, you can change the line style for the border of the axis title. To do so, use the option Custom to select the desired line style. The option None removes the border. |
| If you enable the option Shadow, the axis title will also be highlighted with a shadow. |
▪Fill section
| Here, you can change the fill of the axis title. To do so, use the option Color to select the desired fill color. The fill will be transparent if you use the option None. |
| If you select the fill type Effects and click on the Customize button, the program will display a dialog box that will allow you to also apply more complex fills (such as a color gradient). The use of this dialog box is described in Object properties, Fill tab. |
Text tab
Here, enter the desired axis title. If you delete the text completely from the input field, the axis title, as a chart element, will be removed.
Font tab
On this tab, you can change the formatting of the axis title.
In addition to font, font size, and text styles, you can also set the alignment, rotate the labels and change the numeric format.