A topic is the main subject or idea that a conversation, piece of writing, or discussion focuses on. When your teacher announces that today's topic is the American Revolution, she's telling you what the class will be about. When you choose a topic for your research paper, you're deciding what subject you'll explore and explain.

Topics can be broad or narrow. “Animals” is a very broad topic, while “how octopuses camouflage themselves” is much more specific. Good writers and speakers usually narrow their topics so they can explore them thoroughly rather than skipping across the surface of something too big to handle well.

Today, we use topic in all kinds of contexts: a topic sentence tells readers what a paragraph will be about, while staying on topic means you're sticking to the subject at hand instead of wandering off into unrelated territory.

When something becomes a hot topic, it means many people are discussing it right now. When someone changes the topic during an awkward conversation, they're steering the discussion toward safer ground.