kilo

Kilo is a metric prefix denoting a factor of one thousand (10^3). It is represented by the lowercase letter k when attached to a unit, yielding forms such as kilometer (km), kilogram (kg), and kilowatt (kW). In the International System of Units (SI), kilo- multiplies the unit by 1,000; for example, 1 kilometer equals 1,000 meters, and 1 kilogram equals 1,000 grams. The prefix is always written with a lowercase k to distinguish it from the uppercase K used for kelvin.

Etymology and history: The prefix kilo- comes from the Greek χίλιοι (khilioi), meaning thousand. It was adopted into the metric system in the 18th and 19th centuries and formalized in SI to provide a standard way to express large quantities across science and trade.

Usage notes: Use with grams yields kilograms; the gram is defined as one thousandth of a kilogram. In computing and data storage, kilo- has sometimes been used to mean 1,024 (especially for kilobytes), but this is deprecated in strict SI usage; binary prefixes such as kibibyte (KiB) are now used to distinguish 1024 from 1000.

Common uses and cultural references: In everyday language, kilo frequently denotes a kilogram of mass, especially for food and body weight. In slang, “kilo” can refer to a kilogram of illegal drugs.