anacrusis
One or more notes before the first full bar of a piece, also called a pickup or upbeat.
In Depth
An anacrusis (from the Greek anakrousis, a pushing back) is the note or group of notes that precede the first downbeat of a phrase. These pickup notes create momentum, launching the music toward the first strong beat. Many famous melodies start with an anacrusis rather than on beat one. In notation, the anacrusis bar is shorter than a full bar — it contains only the pickup notes. To balance the structure, the final bar of the piece is often shortened by the same amount. The anacrusis is felt as a breath before speaking, an inhale before the first word. Conductors signal the anacrusis with an upward preparatory gesture.
Auld Lang Syne, Happy Birthday, and The Star-Spangled Banner all begin with an anacrusis — pickup notes are far more common in vocal music than most people realise.