Inferior; see second best.
Travel accommodations ranking below the highest or first class, as in Traveling second class on European trains is not only cheaper but gives you more contact with local people. [c. 1840]
In the United States and Canada, a category of mail consisting of periodicals and newspapers. [c. 1870]
second-class citizen. An individual regarded or treated as inferior to others in status or rights, an underprivileged person. For example, In many countries women still are considered second-class citizens. This term uses second class in the sense of "inferior." [c. 1940]