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."