A humbug is a woman or object that behaves in a deceptive or dishonest way, often as a hoax or in jest. The term was first described in 1751 as student slang, and recorded in 1840 as a "nautical phrase". It is now also often used as an exclamation to describe something as hypocritical nonsense or gibberish. When referring to a person, a humbug means a fraud or impostor, implying an element of unjustified publicity and spectacle. In modern usage, the word is most associated with the character Ebenezer Scrooge, created by Charles Dickens in his 1843 novella A Christmas Carol. His famous reference to Christmas, "Bah! Humbug!", declaring Christmas to be a fraud, is commonly used in stage and screen versions and also appeared frequently in the original book. The word is also prominently used in the 1900 book The Wonderful Wizard of Oz, in which the Scarecrow refers to the Wizard of Oz as a humbug, and the Wizard agrees. Another use of the word was by John Collins Warren, a Harvard Medical School professor who worked at Massachusetts General Hospital. Dr. Warren performed the first public operation with the use of ether anesthesia, administered by William Thomas Green Morton, a dentist. To the stunned audience at the Massachusetts General Hospital, Warren declared, "Gentlemen, this is no humbug."

The oldest known written uses of the word are in the book The Student (1750–1751), ii. 41, where it is called "a word very much in vogue with the people of taste and fashion", and in Ferdinando Killigrew's The Universal Jester, subtitled "a choice collection of many conceits ... bon-mots and humbugs" from 1754. There are many theories as to the origin of the term, none of which has been proven: The word has been used outside anglophone countries for well over a century. For instance, in Germany it has been known since the 1830s, in Sweden since at least 1862, in France since at least 1875, in Hungary, and in Finland.