Which of the following best describes 'harmony' in music?

The best description of 'harmony' in music is indeed the combination of different musical notes played or sung simultaneously. Harmony enriches a piece of music by creating a fuller sound and contributing depth to the melody. When multiple notes are sung or played together, they interact with each other, forming chords that can evoke various emotions and textures. This simultaneous combination allows for complex relationships between the notes, which is a fundamental aspect of many musical styles, from classical to contemporary.

The other options focus on different musical concepts. Patterns of sound and silence relate more to rhythm and structure rather than harmony. The linear succession of musical tones pertains to melody rather than harmony, as it involves the sequence of notes happening one after another. Dynamic levels of sound deal with the volume of music, which is a separate concept from the idea of harmony, which is about how notes work together rather than their loudness or softness.