Definition of Ionian mode in English:

Ionian mode

noun

Music
  • The mode represented by the natural diatonic scale C–C (the major scale).

    • ‘his lesson is on the ionian mode used in music theory for guitar and bass. Modal theory is an important aspect of understanding music theory.’
    • ‘Incidentally, when you write a major scale from the tonic note up to the tonic note, you are also forming a mode, called the ionian mode!’