What is transmission speed?

Transmission speed is also called 'Bit rate'. It's the number of bits that are conveyed or processed per time unit, mostly for telecommunications or computing. bps = bits per second. In order from least to greatest, there's kilobit, megabit, gigabit, and terabit. That's for decimal prefixes. There's also Binary prefixes, but I don't know much about them. By the way, why do you need to know?