Meaning of “theme” - Learner’s Dictionary

theme

noun us uk /θiːm/
The theme of the play is the battle between good and evil.The film has several, overlapping themes.What was the theme of his speech?The war provided the dominant theme of his work.Most of the paintings had religious themes.

B2 [ C ] the subject of a book, film, speech, etc:

The theme of loss runs through most of his novels.
theme music/song/tune

the music that is played at the beginning and end of a particular television or radio programme

(Definition of “theme” from the Cambridge Learner’s Dictionary © Cambridge University Press)