Notes and Octaves
The twelve pitch classes, how they repeat in octaves, and how to name any key on the piano.
Music uses twelve distinct pitches before the pattern repeats: C, C#, D, D#, E, F, F#, G, G#, A, A#, B. On a piano these are the seven white keys plus the five black keys in between.
Play the same letter higher or lower and you get the same note in a different octave — it sounds like "the same note, but higher/lower." Each octave is numbered (C4 is commonly called "middle C"); going from C4 to C5 doubles the frequency.
The distance between two neighboring keys — white to the nearest black, or E to F, or B to C — is called a semitone (half step). Two semitones make a whole tone (whole step). Every scale and interval you'll learn is built by counting semitones.
Try it: click across the keyboard below and watch the note name change. Notice that C, D, E, F, G, A, B repeat every seven white keys, while the black keys interrupt the pattern between E–F and B–C, where there's no black key at all.