Rhythm
Swing
An uneven subdivision that gives paired notes a long-short feel.
In plain English
When music swings, two written eighth notes are not usually played as equal halves of the beat. The first lasts longer and the second arrives later, with the exact ratio changing by tempo and style.
Try or listen for this
Instead of counting two even sounds as “one and,” try feeling them closer to the first and third parts of a triplet.
Why it matters
Swing is a shared rhythmic language. Playing the notes evenly when the music should swing can make an otherwise accurate part feel wrong.