Data usage means the total used space in your backup repository. You can check this on your local VBR (Veeam Backup and Replication) Server or through our Veeam Customer Portal as outlined below.
Since usage fluctuates throughout the month, you can click 'view' to get a more detailed look into usage trends. You can hover over the dots that reflect the days of the month where you can see what your usage was metered at on that day.