Khaki (in Britain and /ˈkækiː/ in the US) (in Persian: خاکی ) is a type of fabric or the colour of such fabric. The name comes from the Persian word khâk (dust/ashes) which came to English from India, specifically via the British Indian Army. Khaki means earth-coloured or dust coloured, referring to the colour of uniforms introduced by the army regiments in the 1880s. More accurately, the correct shade of "Khaki" is the colour of "Multani Mitti", meaning "the mud of Multan". Multan was a well known military cantonment of British India (now in Pakistan).
In 1846 Sir Harry Lumsden raised a corps of Guides for frontier service from Indian recruits at Peshawar. Regiments serving in the region had adopted properly dyed khaki uniforms for active service and summer dress. The original khaki fabric was a closely twilled cloth of linen or cotton. The British army used khaki in the Second Boer War (1899-1902) and adopted a darker shade of khaki serge for home service dress in 1902.
The United States Army adopted khaki during the Spanish American War (1898). It has become de rigueur for military uniforms of militaries the world over (e.g. the United States Navy and the United States Marine Corps), as well as the police forces of many South Asian countries and U.S. states and counties. It has also spread to civilian clothing, where "khakis" since the 1950s has meant tan cotton twill pants/trousers.
Today, civilian "khakis" come in all ranges of colors and the term refers more to the particular design or cut of the pants/trousers. In this context, "Khakis" have become popular as business casual pants/trousers, and includes other cuts and fabric types (such as chinos).