Which term refers to the simultaneous use of two or more tonal centers?

The term that refers to the simultaneous use of two or more tonal centers is polytonality. This musical technique involves layering multiple keys or tonalities at the same time, creating a rich, complex sound. Composers who utilize polytonality often aim for a unique harmonic texture that contrasts different tonal centers, allowing for innovative and varied musical expression.

In contrast, atonality refers to music that lacks a clear tonal center altogether, often moving away from traditional scales and harmonies. Monophony describes a single melodic line without harmonic support or layered tonalities, focusing solely on one voice or instrument. Bitonality specifically involves only two different tonal centers played simultaneously, which is a more limited form of polytonality. Therefore, polytonality encompasses a broader spectrum of multiple tonal centers, making it the most fitting term in this context.