Kilo is a prefix that is used as a multiplier. In the "analog" world, kilo represents the numeric value of 1000 (103); such as a frequency of 20 kHz, which is 20,000 Hz.
When used in the digital world, kilo represents the numeric value 1024 (which is 210); e.g. a bit rate of 8 Kbit/s, which is a rate of 8192 bits per second.
In the analogue world the prefix is written as a lowercase "k", whereas in the digital world the uppercase "K" is used.