1000 bytes. Unfortunately, the term is sometimes also used to mean 
bytes. However, this usage
is deprecated, and the term kibibyte is preferred for
1024 bytes.
Kilobyte
See also
Byte, Kibibyte, Megabyte, Gigabyte, TerabyteExplore with Wolfram|Alpha
References
National Institute of Standards. "Prefixes for Binary Multiples." http://physics.nist.gov/cuu/Units/binary.html.Referenced on Wolfram|Alpha
KilobyteCite this as:
Weisstein, Eric W. "Kilobyte." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Kilobyte.html