A song is a musical work with lyrics, usually accompanied by instruments or vocals. Occasionally, songs are purely instrumental. In any case, a song has a melody and a rhythm, and may contain one or more verses or refrains. In addition, most songs have a meter or beat. Songs often consist of a series of phrases that tell a story or convey a particular mood. Verses can be repeated for artistic effect, or a recurring melodic motif called a bridge is used to build tension before the chorus.
Songs can be written and performed for an audience of any size or may be included in theatrical productions, dance performances, television shows, films, or operas. A song may also be sung a cappella, with an instrumental accompaniment such as an acoustic guitar or piano, or accompanied by a large orchestra.
Generally, musicologists study the characteristics of songs by analyzing acoustic recordings of their performance and compositional structure. In some cases, the study of songs is part of a larger study of music and human behavior.
Some songs have been documented for hundreds of years, starting with the troubadours and bards of Europe, continuing through the lutenists and Elizabethan composers. These early art songs generally have a flowing accompaniment that supports, illustrates, or contrasts with the voice. Later, a more structured form of song emerged with the emergence of opera and other large classical musical forms. These art songs tended to be romantic love songs, often addressed to an ideal or imaginary person.