Axis labels are the text labels that appear along the horizontal and vertical axes of a chart. They can be used to indicate the units of measure for the data plotted on the chart, or to provide descriptive text about the data.

To add axis labels to a chart in Excel, follow these steps:

1. Select the chart that you want to add axis labels to.

2. Click the "Design" tab in the ribbon.

3. Click the "Layout" button, and then click the "Axes" button.

4. Select the "Primary Horizontal" or "Primary Vertical" axis, and then click the "Labels" button.

5. Select the "Text" check box, and then enter the text that you want to appear as the axis label.

6. Repeat steps 4 and 5 for any other axes that you want to add labels to.

7. Click the "OK" button.