Ack or ACK may refer to:
Ackworth is a village and civil parish in the metropolitan borough of Wakefield, West Yorkshire, England, situated between Pontefract, Barnsley and Doncaster on the small River Went.
In computability theory, the Ackermann function, named after Wilhelm Ackermann, is one of the simplest and earliest-discovered examples of a total computable function that is not primitive recursive.
Bernard Stanley "Acker" Bilk, MBE (28 January 1929 – 2 November 2014) was an English clarinettist and vocalist known for his appearance – goatee, bowler hat and striped waistcoat – and breathy, vibrato-rich, lower-register clarinet style.
The ackee, also known as achee, ackee apple or ayee (Blighia sapida) is a member of the Sapindaceae (soapberry family), as are the lychee and the longan.
Ackerson Creek is a stream in Tuolumne County, California, in the United States. It is a tributary of the South Fork Tuolumne River.
The Ackerl Hut (German: Ackerlhütte) is an Alpine club hut in the Wilder Kaiser mountains in Austria. It is run by the Kitzbühel section of the Austrian Alpine Club and lies at a height of 1,455 metres (4,774 ft) (according to other sources 1,456 m or 1,465 m) below the south faces of the Regalmspitze, Ackerlspitze and Maukspitze.
Acker comes from German or Old English, meaning "ploughed field"; it is related to or an alternate spelling of the word acre.
Ackerman House, is located in Saddle River, Bergen County, New Jersey, United States. The house was built in 1811 and was added to the National Register of Historic Places on January 10, 1983.
Ackworth School is an independent school located in the village of High Ackworth, near Pontefract, West Yorkshire, England.