Humbug is language that's either deceptive or just ridiculous. Either way, it's verbal garbage and inspires people to mutter "Bah! Humbug!" — just like Scrooge did in "A Christmas Carol."
Humbug is one of many words in English for language that can't be trusted. Humbug is like snake oil: it's deceptive, tricky, and meant to put one over on you. There's a slightly different type of humbug that refers to nonsense: speech or writing that's silly, pretentious, or just empty. When someone is talking a lot but saying nothing, they're talking humbug.