Baloney is informal American English for something silly, fake, or not true. You say “That’s baloney” when someone is talking rubbish — a soft, almost funny way to call out nonsense, not as sharp as ruder words. Grown-ups use it with children; newspapers use it when they want to sound plain. In this sense it is never the sausage on the sandwich. The sausage is bologna (an Italian sausage); many Americans say and spell that sausage baloney too, and this “nonsense” meaning is probably a jokey offshoot of that, maybe even a polite stand-in for a ruder word. Though actually, the history is not fully settled: some people point instead to old theatre slang (Polari) balonie. Either way, when someone says baloney about an idea, they mean “I don’t believe you.”