To look up means to search for information about something, usually in a reference source like a dictionary, encyclopedia, or website. When you encounter an unfamiliar word while reading, you might look it up in a dictionary to find its meaning. If you're curious about when dinosaurs went extinct, you could look it up online or in a science book.

Today, most people look things up digitally, typing questions into search engines or tapping on their phones.

Looking something up shows curiosity and resourcefulness. Instead of staying confused or making wild guesses, you take action to find accurate information. Scientists, writers, and students constantly look things up, even about topics they know well, because checking facts matters more than pretending to know everything.

The phrase can also mean visiting someone, as in “I'll look you up next time I'm in town,” though this usage is less common today.