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.
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.
Alternatively, a jersey as used in sport is a shirt worn by a member of a team, typically depicting the athlete's name and team number as well as the logotype of the team or corporate sponsor. Cycling jerseys of specific colour or pattern represent certain statuses in cycling, such as the maillot jaune (yellow jersey) of the leader of the Tour de France, or the rainbow jersey. Cycling jerseys are usually made of synthetic microfiber material to aid in wicking sweat away from the skin to allow it to evaporate. The main garment of an ice hockey uniform, which was traditionally called a sweater, is increasingly known as a hockey jersey. This garment, along with basketball jerseys which are usually sleeveless and baseball jerseys which are usually button up, have become fashion accessories. A related term is "bib", which may refer to a shirt (jersey, esp. in Britain), or to an attachment with the player's number.
In some sports, such as baseball, basketball, and American football, a player's jersey may be "retired". When a jersey is retired that player's jersey is placed usually where the team plays in honor of that player's accomplishment. Generally, when a jersey is retired, the number on the player's jersey is made unavailable for future players.