These words refer to a recognizable succession of musical sounds, whether played or sung. Melody may refer to the pleasing or aesthetically satisfying quality of such an entity: a composer noted for his exquisite melodies . Or it can refer neutrally to the leading voice in a musical composition: harmonizing the melody for a four-part choral arrangement. As a generic word, it can refer to one of the three basic ingredients of music, the one pertaining to the linear sequence of intervals: melody , harmony, and rhythm.

Theme refers to a melody or recognizable sequence that is treated in a musical composition by such means as statement, development and recapitulation, or by the addition of variations. In this case, the sequence may occur or recur in any voice or even be spread out among two or more voices: a theme first stated in the cellos and then referred to in fragmentary form by other sections of the orchestra.

Song in its neutral senses usually refers to a melody rendered by the human voice: a song for soprano or tenor; a popular song recorded by the leading vocalist of the day; folk songs performed by the three singers to guitar accompaniment. The word can refer more widely to any rendering of melody : bird songs ; whistling a song . In its most general sense, the word may suggest approval for any sort of lyrical intensity, as of poetry: a poetic tradition rich in song .

Tune is more informal than song and suggests a melody that is simple, direct and catchy: infectious folk tunes . The word may refer to the music, as distinct from the words, of a song : stark words set to a lovely tune . Often, the word suggests songs of less than the highest aesthetic rank: musical comedy tunes ; the grating tunes of singing commercials.

Aria , derived from the Italian word for song , refers to any of the solo songs in an opera or oratorio. The word contrasts the formal organization and lyrical intensity of such a piece with the looser, more low-key passages of recitative that surround it: one long aria about how cruelly he had mistreated her. Air is the exact English counterpart for aria , but is now rarely used except in reference to early English music, often indicating the self-contained simplicity of a folk song rather than the ornate flourishes of a formal piece composed as part of such longer compositions as an opera: Scottish airs and ballads.

Lied is the comparable German word for song , used in English to refer to the art-song form developed by such composers as Schubert and Wolf: the Schubert lied about the beggar man. More often it is used in the plural, referring generically in this case to the German art-song literature or to art songs in general: an evening of lieder .