A gag name is a false name used to elicit humor through its simultaneous resemblance to a real name on the one hand, and to a term or phrase that is funny, strange, or vulgar on the other hand. The source of the humor is the pun and double entendre; frequently, the humor arises when an unknowing victim is induced to use the name without realizing the joke. Urban legend holds that such a prank is often played on substitute teachers or others who must read a roll, for whom pranksters will switch the roll with one containing such names.

Some names that would be considered gag names have been adopted as stage names by performers, often in the adult entertainment industry. Gag names can also be applied to businesses, such as Howard Stern's use of the fictitious Sofa King: in a hoax ad, the store was described as being "Sofa King great" (i.e., "so fucking great"). A January 18, 2000, FCC complaint for using the phrase was dismissed. A similar sketch was performed on Saturday Night Live in early 2007, portraying Sofa King as a new store opening after the success of Mattress King.