An octave is a special interval in music where two notes sound remarkably similar even though one is higher than the other. When you play a C note on a piano and then play the next C note up the keyboard, those two notes are an octave apart. They have the same name and the same musical quality, but one sounds higher.

Starting from middle C on a piano, you'd count: C, D, E, F, G, A, B, C. That's eight notes, and you're back to C again, just higher.

Your voice naturally moves in octaves when you sing. Women and men often sing “the same song” but in different octaves because their voices have different ranges. When a choir sings in octaves, some voices sing higher and some lower, but they're all singing the same melody, creating a rich, full sound.

Scientists have discovered why octaves sound so similar: the higher note vibrates twice as fast as the lower one. This mathematical relationship makes octaves sound harmonious and natural to our ears, which is why nearly every musical culture in the world recognizes and uses them.