The Ionian mode starts on the 1st degree of the scale of C major.
This mode is the same as the major scale.
The pattern is Tone - Tone - Semitone - Tone - Tone - Tone - Semitone.
The semitones are between the 3rd & 4th and 7th and 8th degrees of the scale
Music that uses the Ionian mode is bright sounding.
It is well known for its use in pop, rock, classical, jazz, punk etc ..
Major scales are versions of the Ionian mode from different starting notes.