Suz is exactly right. The name "jersey" actually comes from the Isle of Jersey, one of the Channel islands between England and France because that's where the fabric was first produced. Single-knit jersey is very stretchy and is characterized by a smooth surface on one side and little bumps on the reverse side. Double-knit jersey sandwiches the bumpy sides in the middle so both the front and back are smooth. The original wool jersey was used mainly for undergarments, but it was Coco Chanel (along with other designers) who started using the fabric made in other fibres like silk and cotton because she liked the way it draped and handled. Those fabulous, slinky, bias-cut gowns worn by stars like Jean Harlow in the 30s and 40s were often made of silk jersey.