A round neckline with a ribbed texture.
(by extension) A shirt, sweater, or similar garment with such a neckline.
Referring to the collar of pullover garments and usually of sweaters and T-shirts, when [the collar] circles the neck. Often crew necked.
Referring to a collar, whose front is meant to ride up onto the neck, sometimes to Adam's apple level, more often termed as high crew.