In music theory, an interval is the relationship between two notes or pitches, the lower and higher members of the interval. It often refers to those two notes themselves.
Larger intervals are described as wide and smaller ones as narrow (for example, a sixth is wider than a third), but these are only relative terms.

Intervals may occur two ways:

vertical (or harmonic) if the two notes sound simultaneously
linear (or melodic), if the notes sound successively.

exercise 1: unison, major/minor second , major/minor thirds
exercise 2: unison, perfect fourth , perfect fifth, octave
exercise 3: second, third, sixts ans seventh (minor and major)
exercise 4: unison, fourth, fifth, octave - (perfect, diminished , augmented )
exercise 5: all intervals

Including many other ear training exercises based on intervals