The term 'Sack Dress' is a type of dress that was popular in the 1920s. It is characterized by its loose, shapeless silhouette and lack of waistline. The term 'PAJAMAS' is also used to describe this style of dress, as it was often made from lightweight fabrics such as silk or cotton. The term 'Sack Dress' is derived from the French word 'sacque, ' which means 'BAG.' This style of dress was popularized by Coco Chanel and other fashion designers of the time.