Acorna is a "Unicorn Girl", a fantasy fiction character created by Anne McCaffrey and Margaret Ball in their novel Acorna: The Unicorn Girl (1997). Acorna is also one name for the Acorna Universe series: ten fantasy or science fiction novels by McCaffrey and Ball (the first two) or McCaffrey and Elizabeth Ann Scarborough (eight more, 1999 to 2007). The Acorna series is a sub-set of the Federated Sentient Planets Universe.