Middle C is so called because it is the only of the eight C keys on the piano keyboard that is located in the center of the keyboard. In musical notation, that note is also located in between the bass and treble clefs staves.
To convert sound waves into mechanical waves
A credit note is another name for and adjustment note
Middle C sits in the middle of the grand staff. It is usually depicted on the treble clef staff but can also be written on the bass staff.
One quarter note
Ti-ri-ti-ri
ledger
In order from highest to lowest, the common clefs are:
Treble
Alto
Tenor
Bass
4/4
E
Letter C in apex