A hackney or hackney carriage (also called a cab, black cab, hack or London taxi) is a carriage or car for hire. A hackney of a more expensive or high class was called a remise.

In the United Kingdom, the name hackney carriage today refers to a taxicab licensed by the Public Carriage Office, local authority (non-metropolitan district councils, unitary authorities) or the Department of the Environment depending on the region of the country.

London Black cabs come under the remit of TFL.

Though there has never been a law requiring London’s taxis to be black, they were, since the end of the Second World War, sold in a standard colour of black. This, in the 1970s gave rise within the minicab trade to the nickname ‘black cab’ and it has become common currency. However, before Second World War, London’s cabs were seen in a variety of colours. They are produced in a variety of colours, sometimes in advertising brand liveries.

In London, hackney-carriage drivers have to pass a test called The Knowledge to demonstrate that they have an intimate knowledge of the geography of London streets, important buildings, etc. Learning The Knowledge allows the driver to become a member of the Worshipful Company of Hackney Carriage Drivers. There are two types of the badge, a yellow one for the suburban areas and a green one for all of London. The latter is considered far more difficult. Drivers who own their cabs as opposed to renting from a garage are known as “mushers” and those who have just passed the “knowledge” are known as “butter boys”. There are currently around 21,000 black cabs in London, licensed by the Public Carriage Office