The total amount of outbound traffic from a website*, typically measured in gigabytes (Gb).
* typically excludes email.
The difference between bandwidth and data transfer causes much confusion and is worth noting.
Bandwidth is a rate and data transfer is a total. For example, you might buy bandwidth of 128 kbps for a maximum monthly data transfer of roughly 40 GB.
|128 kbps||= bits||= bytes|
|divide by one billion
Note: many hosts use the terms bandwidth and data transfer interchangeably, referring to a monthly data allowance as bandwidth.
see also: Web Hosting Tools
Data Transfer FAQ