Young College Girl Wearing Sport Jersey

A jersey is an item of knitted clothing, traditionally in wool or cotton, with sleeves, worn as a pullover, as it does not open at the front, unlike a cardigan. It is usually close-fitting and machine knitted in contrast to a guernsey that is more often hand knit with a thicker yarn. The word is usually used interchangeably with sweater and is the name always officially used in the United Kingdom to refer to the item when worn as part of the uniform of military, police or other uniformed personnel.
History
Jersey, in the Channel Islands, was famous for its knitting trade in medieval times, and because of that original fame, the name jersey is still applied to many forms of knitted fabric, round or flat. The traditional jersey, and traditional guernsey, are dyed a navy blue colour, using a dye that does not require stripping the wool of its natural oil, rendering these sweaters surprisingly water resistant. The wool used in guernseys is often passed through oil in order to render it doubly water-resistant.