What characterizes an "atonal" piece of music?

Atonal music is characterized by the absence of a tonal center or key, which distinguishes it from traditional tonal music that typically revolves around a home key. In atonal compositions, no single pitch holds prominence or serves as a reference point for harmonic relationships, resulting in music that does not adhere to conventional structures of major or minor scales. This lack of tonal center allows composers to explore a broader range of sounds and expressions without being constrained by the rules of tonality.

In contrast, defining scales and harmonic progressions are fundamental elements of tonal music, while reliance on rhythmic patterns alone does not encompass the complexity of atonal works. In atonal music, rhythm can still play a vital role, but it exists independently from tonal considerations, allowing for a more abstract and innovative approach to composition.