A convention is an accepted way of doing something that most people follow, even though it's not a law or rule that must be obeyed. In English writing, it's a convention to capitalize the first word of a sentence. Nobody will arrest you for writing “the dog ran fast,” but readers expect “The dog ran fast” because that's the convention everyone learned.

Conventions exist everywhere. In conversation, it's a convention to say “hello” when you meet someone and “goodbye” when you leave. At a formal dinner, there are conventions about which fork to use first. In music, composers follow conventions about how to write notes on a staff. These aren't rigid rules, they're just patterns that developed over time because they work well and help people understand each other.

The word can also mean a large gathering of people who share an interest. A comic book convention brings together thousands of fans, artists, and collectors. Political parties hold conventions to nominate candidates for president. Scientists attend conventions to share their latest discoveries. At these events, people dress up, attend presentations, meet others who share their passions, and learn new things.

Breaking conventions on purpose can be creative or rebellious. Artists might ignore painting conventions to create something startling and new. But understanding conventions first usually helps: you need to know the conventions before you can break them effectively.