Outside of the plot, the 'theme' is often used to describe a topical issue that runs through the story, for example, fatherhood, unrequited love, racism. But it can also be more subtle, - that which colours the plot, sets its tone, gives it context, for example, water, the sky, sex, and can often be found in the story's imagery and metaphors.
or
The central idea or concept in the story (Sometimes could be the conflict of the story too)
In some places, theme could mean an authors message. What point is the author trying to get across? Ex: Don't judge a book by it's cover (don't judge a person by how the look)
theme is the truth about life that a story reveals
"Theme is the central message of a literary work. It is not the same as a subject, which can be expressed in
a word or two: courage, survival, war, pride, etc. The theme is the idea the author wishes to convey about
that subject. It is expressed as a sentence or general statement about life or human nature. A literary work
can have more than one theme, and most themes are not directly stated but are implied. The reader must
think about all the elements of the work and use them to make inferences, or reasonable guesses, as to
which themes seem to be implied." (from Laying the Foundation series of books published by AP
Strategies in Dallas)
For example, if love is a topic/subject of two novels, a major theme in one of the novels could be "Love, if
taken to extremes, can be negative rather than positive," while in the other novel, the theme might be "Love
can conquer even the greatest evil." Notice that the topic/subject is the same, but the messages about that
topic/subject are different in different works.
Consider this:
A theme is a meaning of a work. (Yes, there can be more than one "meaning.") Can the meaning of a work
be love? hate? greed? No-that makes no sense! Those are just topics, not themes. The theme is the
statement an author is making about a topic.
To find it, just look for the main idea.
A theme is the writer's message about a topic.
Some examples of themes are: honesty, acceptance, don't be greedy, treat others the way you want to be treated, beauty is only skin deep, love others, don't boast, don't think you are better than others.