A guinea pig is a small, furry rodent that people often keep as a pet. Despite the name, guinea pigs aren't pigs and they don't come from Guinea (a region in Africa). They're actually from South America, where they were first domesticated thousands of years ago. Guinea pigs are gentle animals with round bodies, short legs, and no visible tail. They make squeaking sounds when they're excited, especially when they hear their food being prepared.

The phrase guinea pig also means a person or animal used to test something new or experimental. When a teacher tries out a new teaching method on one class before using it with everyone else, those students might joke that they're the guinea pigs. If you volunteer to be the first person to try your friend's unusual recipe, you're being a guinea pig.

This second meaning doesn't have to be negative. Sometimes being a guinea pig means getting early access to something exciting, like testing a new video game before it's released. But it can also mean taking a risk that others aren't willing to take yet, since you're trying something that hasn't been fully proven to work.