Mx (title)

Mx, usually pronounced /ˈməks/, /ˈmɪks/ or /ˈmʌks/ (miks or muks), is an English-language honorific for use alongside Mr, Ms, etc. that does not indicate gender. It is often the only option for nonbinary people, as well as those who do not wish to reveal their gender. It is a gender-neutral title that is now widely accepted by the British government and many businesses in the United Kingdom.

The word was first proposed in the late 1970s. The "x" is intended to stand as a wildcard character (cf. 'Tx' in electronics, short for 'transmit'), and does not imply a "mixed" gender.

In 2013 Brighton and Hove City Council in Sussex, England, voted to allow its use on council forms, and in 2014 the Royal Bank of Scotland included the title as an option. In 2015, recognition spread more broadly across UK institutions, including the Royal Mail, government agencies responsible for documents such as passports and driving licences, most major banks, several other companies, and UK charity Battersea Dogs & Cats home.

...
Wikipedia