Theme (music)
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In music, a theme is the beginning or main melody. It is usually familiar sounding and able to be recognized when it is heard.
From that beginning part of the music, variations can be played as the composition is developed or put together.
The phrase theme song (British English: theme tune) may also be used to refer to a signature song that has become especially associated with a particular performer or dignitary, often used as they make an entrance.