Turtleneck sweater

A polo neck, roll-neck, (UK), turtleneck (US, Canada), or skivvy (Australia, New Zealand) is a garment—usually a sweater—with a close-fitting, round, and high part similar to a collar that folds over and covers the neck. It can also refer to type of neckline, the style of collar itself, or be used as an adjective ("polo necked").

A simpler variant of the standard polo neck is the mock polo neck (or mock turtleneck), that resembles the polo neck with the soft fold at its top and the way it stands up around the neck, but both ends of the tube forming the collar are sewn to the neckline. This is mainly used to achieve the appearance of a polo neck where the fabric would fray, roll, or otherwise behave badly unless sewn. The mock polo neck clings to the neck smoothly, is easy to manufacture, and works well with a zip closure.

Polo neck-like garments have been worn for hundreds of years, dating at least to the 15th century.

From the late 19th century on, polo necks were commonly worn by menial workers, athletes, sailors and naval officers. Since the middle of the 20th century black polo necks have been closely associated with radical academics, philosophers, artists and intellectuals. The polo neck jumper became an iconic symbol of the French philosopher Michel Foucault. Polo necks also became a big fashion for young wealthy men after they were worn by European film stars Marcello Mastroianni and Yves Montand. The term polo neck, common in British English, is thought to derive from garments with similar necklines worn by polo players.

Greta Garbo often wore polo necks and trousers privately, as later Audrey Hepburn would do in official photographs.

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Wikipedia