A measurement of digital information storage or transmission, and a multiple of the unit "bit" using the International System of Units prefix.
The kilobit is 10^3 bits, or 1000 bits. A kilobit is equal to 125 bytes.
Kilobits are pretty much only ever used to describe download and upload speeds for broadband, mobile data and dialup services.
For example, many ISPs will sell broadband packages of 15Mbit/s (megabits) downstream and 5Mbit/s upstream.
Therefore, to calculate how fast your actual download speeds will be, in bytes, you must divide those figures by 8. 15mbit/s = 1.875 MB (megabytes) per second.
Very similar to kibibits, which use a more exact prefix established by the International Electrotechnical Commission.