What3words (stylized as what3words) is a proprietary geocode system designed to identify any location on the surface of Earth with a resolution of approximately 3 metres (9.8 ft).

[5] What3words has been subject to a number of criticisms both for its closed source code[6] and the significant risk of ambiguity and confusion in its three word addresses.

He credits a mathematician friend for the idea of dividing the world into 3-metre (10 ft) squares, and the linguist Jack Waley-Cohen with using memorable words.

[17] What3words originally sold "OneWord" addresses, which were stored in a database for a yearly fee,[11] but this offering was discontinued[18] as the company switched to a business-to-business model.

[29][14] In a 2019 blog, open standards advocate and technology expert Terence Eden questioned the cultural neutrality of using words rather than the numbers generated by map coordinates.

[8] In September 2022, the Department for Culture, Media and Sport used What3words to direct mourners to the end of the queue to view the Queen lying in state in London.

Of the first five codes published, four led to the wrong place,[32] including a suburb of London some 15 miles from the real end of the queue.

[33] Officials later moved to an automated system to generate the identifiers, as they realised having people involved in the process resulted in typos.

[7] According to Rory Sutherland from the advertising agency Ogilvy in a 2014 op-ed piece for The Spectator, the system's advantages are memorability, accuracy, and non-ambiguity in speech.

When approached by Cambridge News, the Ambulance Service continued to recommend the app, and did not respond to a query about why they were unable to quickly pinpoint the precise location using the system.

[6] The company has pursued a policy of issuing copyright claims against individuals and organisations that have hosted or published files of the What3words algorithm or reverse-engineered code that replicates the service's functionality, such as the free and open source implementation WhatFreeWords; the whatfreewords.org website was taken down following a Digital Millennium Copyright Act (DMCA) take-down notice issued by What3words.