An agent is someone who acts on behalf of someone else, representing their interests and making decisions for them. When an author has a literary agent, that person negotiates book deals, reviews contracts, and handles business matters so the author can focus on writing. A travel agent helps people plan trips and book flights. A sports agent represents athletes, negotiating salaries and endorsement deals with teams and companies.

The key idea is that agents have the authority to act for the people they represent. When your parents can't attend a parent-teacher conference, they might designate a relative as their agent to go in their place. That person can speak for your parents and make decisions they would make.

In science, an agent is something that produces an effect or causes change. A cleaning agent is a substance that removes dirt. A chemical agent might cause a reaction. Scientists studying diseases look for the infectious agent, the bacteria or virus that causes illness.

When someone describes themselves as a “free agent,” they mean they're not tied to any particular organization and can act independently.