The density of a sound or a work refers to the number of parts that are sounded simultaneously, that is, to its complexity. Expressions such as or 'light' and 'thin' are commonly used to describe textures with lesser densities, and 'thick' and 'heavy' are commonly used to describe textures with greater densities.
Density often varies throughout a work, especially longer and more complex ones. Such variation is an important factor in making music interesting, as is variation in volume, rhythm and instrumentation.