Relevant means connected to what matters right now or what you're dealing with. When information is relevant, it has a real relationship to the question at hand.

If your class is discussing Abraham Lincoln and you bring up facts about George Washington, that's not particularly relevant. But if you mention Lincoln's views on slavery during a discussion about the Civil War, that's highly relevant because it connects directly to the topic.

The opposite of relevant is irrelevant. If your friend asks whether you finished your homework and you start talking about your favorite video game, you're giving an irrelevant answer.

In science class, only relevant data helps answer your experimental question. If you're testing whether plants grow faster with more sunlight, measuring the plants' heights is relevant. Measuring their smell is probably irrelevant.

When you're researching a paper or solving a problem, learning to identify what's relevant and what isn't saves a lot of time and helps you think more clearly.