Broadband speed is measured in megabits per second, commonly stated as Mb or Mbps (i.e. 15 Mb or 15 Mbps). Costs for bandwidth are typically compared as megabits per second per month or Mbps/mo.
There are eight bits in a byte, so, if your download speed is 8 megabits per second (8 Mbps), then that's actually sending the rough equivalent of 1 megabyte per second (1 MBps).
Make sure you don't get confused between megabits and megabytes (which tends to be written as MB or GB when referring to gigabytes).
It's an important distinction because the size of many files, including songs, photos, and movies, are described in megabytes, as are download allowances. Download allowances are known as data caps. Data caps are typically expressed as the total number of megabytes that can be downloaded in a monthly billing period. If a data cap is exceeded additional charges may be added by the service provider.
You may also see Kb and KB - kilobits and kilobytes; there are 1,024 KB in a MB, and 1,024 MB in 1 GB - the same is true for Kb/Mb/Gb. There are roughly 1000 Kbps in a 1 Mbps stream and there are 1000 Mbps in a 1 Gbps stream. So, a gigabit per second service is 1 million times faster than a 1 kilobit service.