Intervals is the distance from one pitch to another

From C to C# = half step (h) or a semitone (st)
From C to D = Whole step (W) or a Tone (T)

Intervals on a Piano

Intervals table

Semitones	Interval	Short
0	Perfect Unison	P1
1	minor 2nd	m2
2	Major 2nd	M2
3	minor 3rd	m3
4	Major 3rd	M3
5	Perfect 4th	P4
6	Tritone	TT
7	Perfect 5th	P5
8	minor 6th	m6
9	Major 6th	M6
10	minor 7th	m7
11	Major 7th	M7
12	Pefect Octave	P8