anacrusis detail
One or more notes that precede the first full measure of a piece, also called a pickup or upbeat, creating forward momentum into the downbeat.
In Depth
An anacrusis (from Greek "anakrousis," meaning a pushing back) consists of one or more notes that come before the first strong beat of a phrase or piece. These pickup notes create a sense of forward motion and anticipation that propels the music into its first full measure. The anacrusis is complemented at the end of the piece by a shortened final measure — together, the pickup and final measure equal one complete bar.
Some of the most famous melodies in Western music begin with an anacrusis: "Happy Birthday" starts on the upbeat, as do the openings of Beethoven's Symphony No. 5, "The Star-Spangled Banner," and the Beatles' "Yesterday." The German term Auftakt (upbeat) is also widely used. In conducting, the anacrusis requires a preparatory gesture that communicates the tempo and character before the first note sounds — one reason why the opening of a piece is one of the most revealing tests of a conductor's skill.
Beethoven's Fifth Symphony begins with the most famous anacrusis in history — those three short notes before the long note are technically a pickup, not the downbeat, which is the long note itself.