crew neck

Short definition from Wiktionary

Adjective

1. 1
   Referring to the collar of pullover garments and usually of sweaters and T-shirts, when [the collar] circles the neck. Often crew necked.
2. 2
   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.

Noun

1. 1
   A round neckline with a ribbed texture.
2. 2
   A shirt, sweater, or similar garment with such a neckline.