second class (Adjective) — Of inferior status or quality. ex. "a second-class citizen" ex. "second-class accommodations"
second class (Noun) — Not the highest rank in a classification.
second class (Noun) — Not the highest quality in a classification.
second class (Noun) — A class of accommodations on a ship, train or plane that are less expensive than first class accommodations.
second class (Adverb) — By second class conveyance. ex. "we travelled second class"