A (musical note)

La or A is the sixth note of the solfège. "A" is generally used as a standard for tuning. When the orchestra tunes, the oboe plays an "A" and the rest of the instruments tune to match that pitch. Every string instrument in the orchestra has an A string, from which each player can tune the rest of their instrument.
A0 is the lowest note on the standard piano. The octaves follow A1, A2, etc.. A7 is a few pitches lower than C8, the highest note on the standard piano. The note "A" is not considered to be a certain milestone or mark to hit with voice as, for example, Tenor C is, but it can be extremely demanding in certain octaves.