What do you mean by data usage?

Usage includes all the data that you receive (download) or send (upload). If you access the Internet through your home Wi-Fi network using any device (including smartphones), that will be included in your data usage.
This includes software update requests, email notifications, and resend requests. Individual usage results may vary based on the applications you use and the content you access. For example, if your emails have large attachments, the usage for that application may exceed what we have estimated in the data calculator.  See the online Data Calculator and instructional videos for further information.