A bit is a single numeric value, either '1' or '0', that encodes a single unit of digital information. A byte is a sequence of 8 bits.

Usually, data communication speed is measured in bits/kilobits/megabits per second, while storage space is measured in bytes/kilobytes/megabytes.

In data communications, a Kilobit is one thousand bits. It is used to measure the amount of data transferred per second. Kilobits per second is shortened to kb/s, Kbps or kbps (as opposed to KBps, which is Kilobytes per second. Note the capitalization). The lowercase b is commonly used to denote bits, while the uppercase B is used for bytes.

1 kb/s = 1000 bits per second
1 KB/s = 1024 bytes per second

For additional information on bits/bytes check out this article: Bits, Bytes and Bandwidth Reference Guide, or the SG Bits/Bytes Conversion Calculator.