a measurement of how fast data is moved from one place to another. A 56.6 kbps (kilobit-per-second) modem should be able to move 56,600 bits per second of information. In reality though, dial-up connections range quite below this.
The measurement units reflecting the speed of data transfer. Think miles-per-hour for online connections. The standard modem for dial-up connections allows for a maximum of 56 kilobits per second.