Another name for A### is C, which has the same note pitch / sound, which means that the two note names are enharmonic to each other.
It is called triple-sharp because it is 3 half-tone(s) / semitone(s) up from the white note after which is is named - note A.
Middle C (midi note 60) is shown with an orange line under the 2nd note on the piano diagram.
These note names are shown below on the treble clef followed by the bass clef.
1. Piano key note names
This step shows the white and black note names on a piano keyboard so that the note names are familiar for later steps, and to show that the note names start repeating themselves after 12 notes.
The white keys are named using the alphabetic letters A, B, C, D, E, F, and G, which is a pattern that repeats up the piano keyboard.
Every white or black key could have a flat(b) or sharp(#) accidental name, depending on how that note is used. In a later step, if sharp or flat notes are used, the exact accidental names will be chosen.
The audio files below play every note shown on the piano above, so middle C (marked with an orange line at the bottom) is the 2nd note heard.
2. A-triple-sharp note
This step shows note A-triple-sharp in two different positions on the piano, and describes the note characteristics.