Theme or Topic - what's the difference? Are they synonyms?
There is a slight difference between a theme and a topic.
Both can mean the main subject of a talk, piece of writing, film, etc:
The theme of this discussion is education.
The topic for discussion today is education.
You may have heard the expression "stay on topic". Anything with a "topic" usually sticks fairly rigidly to that subject. We tend to use the word with factual subjects rather than fictional works.
However, "theme" can also be used in a much looser way. It can mean a specific subject or a broader idea that recurs or runs throughout something. For example, a film or movie might deal with many different subjects yet have a recurring theme. Anthologies of short stories may feature many pieces by different authors, all in different settings, but all share a common theme that is touched on to varying degrees within each piece.