Each note can occur at various octaves. The exact octave of a note can be indicated using octave numbers. Octaves are numbered starting on C.
The lowest C is C1.
The range of a piano keyboard is from A0 to C8.
Middle C is the name given to C4. Middle C is a pitch that most instruments, high to low, can play and is considered to be in the middle of the range of instrument pitches.
Middle C is the link between the treble and bass clefs. It sits on an imaginary line just above the bass clef and just below the treble clef.
This line, called a ledger line, is drawn through the notehead when needed.
Middle C is the C below A440.