theoretical key

noun1

1. •
   A key signature which has eight or more sharps or seven flats. In music using twelve-tone equal temperament its pitch coincides with its enharmonic, while in most other equal temperament tunings most enharmonic equivalences between key signatures regularly go beyond simple sharps and flats.

   • G-sharp major is a theoretical key with 8 sharps; in 12-tone equal temperament it is enharmonic to A-flat major, but in most other tunings, such as 31-tone equal temperament, it is a distinct key.