Bandwidth (also referred to as transfer) is the amount of data that your web site sends in a month.
Each character that your website sends out takes up a byte. Images can be as large as 100,000 bytes, and downloads can easily reach sizes of 10,000,000 bytes. To that end, bandwidth transfer per month is allocated by gigabytes - one gigabyte is 1 billion bytes.
If your site does exceed your monthly bandwidth allowance, overarge charges are billed on the 1st of each month at the rate of $1.00 per extra gigabyte of transfer.