Octave

Octave is the interval at which the root note rings at a frequency exactly double than that of the root note itself.

For eg. The open 'E' and when fretted at the 12th is also 'E' but an octave higher. On a similar note if we have 24fret guitar, if we fret at the 24th we would get another octave even higher. Over a single string, we can get 2 octaves.

The octave is divided into 12 smaller intervals, that are the semitones. In practice, one fret distance corresponds to one semitone, making an octave consist of 12 semitones.

The 12 semitone notes are C,C#/Db,D,D#/Eb,E,F,F#/Gb,G,G#/Ab,A,A#/Bb,B and starting over again

A whole tone is equal to 2 semitones, thereby making an octave made up of 6 whole tones.