Definition of "Theme" :

noun: a unifying idea that is a recurrent element in literary or artistic work

"It was the usual boy gets girl' theme."

noun: (linguistics) the form of a word after all affixes are removed

noun: an essay (especially one written as an assignment)

noun: the subject matter of a conversation or discussion

"His letters were always on the theme of love."

noun: (music) melodic subject of a musical composition

"The theme is announced in the first measures."

verb: provide with a particular theme or motive

"The restaurant often themes its menus."