The term bandwidth can take on many meanings. In the case of AT&T products and services, the term bandwidth is commonly used when referring to computer networking and measuring Internet usage.
The amount of Internet usage is displayed in upload and downloads amounts. This would commonly be known as the amount of bandwidth the User used during a particular time. There are some carriers that will limit the amount of "bandwidth" a User can use on a monthly basis before penalizing them. AT&T Internet service usage is not limited to a particular size (amount).