Why do we use the letter 'K' for a 'Thousand'?

The video introduces the common use of 'K' to represent a thousand in various contexts like 1k, Y2K, or 10k, signifying a thousand units, the year 2000, or ten thousand pounds, respectively.

The letter 'K' comes from 'kilo,' which is derived from the Greek word 'chilioi,' meaning one thousand. 'Chilioi' and 'thousand' were used interchangeably, similar to 'big' and 'large'.

'Chilioi' was adopted by a French researcher in 1795, evolving into 'kilo' and introduced into the metric system in 1799. 'Kilo' was officially assigned the symbol 'k' in the SI prefixes (International System of Units), representing anything with a value of a thousand.

'Kilo' is used in terms like kilogram, kilometer, and kiloliter, always meaning a thousand units of that measurement. The video discusses the nuances of language, noting that while '10k' can refer to ten thousand pounds with a currency symbol, or a '10k run' implies ten kilometers, it's technically an abbreviation and relies on context for understanding.

The letter 'K' is used for a thousand because it is the SI symbol for 'kilo,' which means a thousand units, thanks to its Greek origins and adoption by a French researcher.