Carina: A keel or ridge.*
These paperwhites (Narcissus papyraceus) have keeled flower stalks with a prominent ridge running the length of each side. Paperwhites are commonly forced to bloom indoors in the winter to bring a bit of cheer and a lot of fragrance.
*Harris, J.G., Harris, M.W. (2001). Plant identification terminology: An illustrated glossary (2nd ed.). Spring Lake: Spring Lake Publishing.