ruga

A fold, crease, or wrinkle, as in the lining of the stomach.

In zoöl., anat., and botany, a fold, ridge, or wrinkle; a crease or plait; a corrugation: variously applied, as to folds of mucous membrane or skin, the cross-bars of the hard palate, the wrinkles on a shell or a bird’s bill or an insect’s wing-covers, etc.: usually in the plural.

A wrinkle; a fold.

a crease or wrinkle

(anatomy) a fold or wrinkle or crease