The quarterdeck is a raised deck behind the main mast of a sailing ship. Traditionally it was where the captain commanded his vessel and where the ship's colours were kept. This led to its use as the main ceremonial and reception area on board, and the word is still used to refer to such an area on a ship or even in naval establishments on land. Many such facilities have areas decorated like shipboard quarterdecks.

In the 20th century the word came to be applied to the area at the stern of the ship, often (on naval vessels) used for secondary weapons and (on battleships) seaplane catapults. In modern military designs the stern has been roofed over by the helicopter deck but a large space remains underneath which is typically used for sonar equipment or small boats and which is still referred to as the quarterdeck in Commonwealth navies.