音乐，广义而言，就是指任何以声音组成的艺术。英文Music一词源于古希腊语的μουσική（mousike），意即缪斯（muse）女神的艺术。而中文的音乐二字，许慎《说文解字》解释为「音，声也。生于心，有节于外，谓之音。」认为音乐和声音的区别，在于音乐需要透过人心去想像和创造。音乐可分为创作、演奏、聆听三个过程，在不同文化和社会，对于音乐的过程及其重要性都有不同的理解。例如在西非鼓乐里，每个人皆是参与者，人们不会区分作曲者、演奏者和聆听者的身份。

至于何谓声音、噪音和音乐的区别，没有公认的标准。因为音乐和数学、物理相关，欧洲自古希腊时代开始，有人论述乐理。在西方乐理中，音乐的主要元素有音高（或声音的频率）、节奏和音色。不同的音高重叠形成和声，音高依据节奏进行成为旋律，常用的音高形成音阶和调性，规律性的强拍和弱拍形成节拍，拍子的快慢构成速度。但近代有不少音乐家不认同传统的理解，例如二十世纪美国作曲家约翰·凯吉认为任何声音和静默皆是音乐。音乐可以分为不同种类，但每种种类的区别常常是含糊和具争议的。

Music is an art form and cultural activity whose medium is silence and sound. The common elements of music are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics (loudness and softness), and the sonic qualities of timbre and texture (which are sometimes termed the "color" of a musical sound). Different styles or types of music may emphasize, de-emphasize or omit some of these elements. Music is performed with a vast range of instruments and with vocal techniques ranging from singing to rapping, and there are solely instrumental pieces, solely vocal pieces (such as songs without instrumental accompaniment) and pieces that combine singing and instruments. The word derives from Greek μουσική (mousike; "art of the Muses"). In its most general form, the activities describing music as an art form include the production of works of music (songs, tunes, symphonies, and so on), the criticism of music, the study of the history of music, and the aesthetic examination of music. Ancient Greek and Indian philosophers defined music as tones ordered horizontally as melodies and vertically as harmonies. Common sayings such as "the harmony of the spheres" and "it is music to my ears" point to the notion that music is often ordered and pleasant to listen to. However, 20th-century composer John Cage thought that any sound can be music, saying, for example, "There is no noise, only sound."