A criminal is someone who breaks the law, whether by stealing, vandalizing property, hurting others, or committing other acts that society has decided to prohibit and punish. When someone commits a crime, they become a criminal. A person who shoplifts candy from a store is technically a criminal, as is someone who robs a bank or hacks into computer systems.

The word carries serious weight. While everyone makes mistakes, being called a criminal means you've crossed a line from ordinary misbehavior into actions the law specifically forbids. A student who forgets their homework isn't a criminal, but one who breaks into the school after hours is.

Societies need laws to function, and criminals are people who've decided, whether thoughtlessly or deliberately, to violate those rules. Some crimes are minor, like littering or speeding. Others, like assault or burglary, cause real harm to victims and communities. The justice system exists to determine guilt, assign punishment, and hopefully prevent future crimes.

The word criminal can also work as an adjective describing actions or situations: criminal behavior, a criminal organization, or even criminal negligence when someone's carelessness is so extreme it breaks the law. When people say something is “practically criminal,” they mean it feels terribly wrong, even if it's technically legal.