Definition of theme

A theme is a kind of melody whose definition depends on the style of music. However, it is often a phrase that is important to the piece.¹² Wikipedia says that it is "usually a recognizable melody upon which part or all of a composition is based".

In a Bach fugue, it is the "subject".

Examples

Aryll's Theme

From "The Legend of Zelda: The Wind Waker". This theme is utilized for Link's sister, Aryll. Here's the original, but it ends up being transformed to fit many contexts.

Here's a variation of the theme that plays when Aryll is kidnapped. The middle line is the melody from the original with a more intense rhythm.

Here's another variation of the theme. It's a reharmonization with a driving rhythm and harmonic motion. It's played when Link is going to give chase to the kidnapper.

When Link releases he cannot rescue his sister, this variation of the theme is played.