The character or characters go by a single name, with no family/clan/whatever identifier. Unlike No Full Name Given, it's not that their full name is never made known to the viewer. The full name simply does not exist. Cher is an oft-cited example.
Truth in Television for most of history. Bynames, epithets, and family names were used only when necessary to distinguish between people with the same name. In much of the world, having multiple names is a relatively recent invention.
Sometimes appears in translations involving a Dub Name Change when it didn't in the original, such as Beetle Bailey being called just "Masi" in Finnish. This could be seen as going under Only Known by Their Nickname, but not when the character is addressed both on a First-Name Basis and Last-Name Basis in the original and the translation uses the one name for both.
Contrast I Have Many Names, Repetitive Name (when someone's first name and last name are the same) and compare Everyone Calls Him "Barkeep" for an extreme example. Sometimes happens with Stage Names.
Not to be confused with the similar-sounding First-Name Basis or Only Known by Their Nickname.
