topic
[C/U] Both
pl: topics
This word carries a sense of containment and focus, acting as a boundary for a discussion to prevent it from drifting. It is the anchor that keeps a conversation on track, suggesting a deliberate choice of what to address among many possibilities. In academic or professional settings, it is more neutral than a theme, which often implies a deeper, recurring symbolic meaning. A topic is simply the matter at hand, whether it is a light chat about the weather or a complex lecture on quantum physics.
Countable when referring to a specific subject of discussion like a lecture topic. Uncountable when referring to the general nature of the subject matter being discussed.