The idiom "guinea pig" is used to refer to a person who is used as a test subject for a new product, experiment, or idea. It comes from the fact that guinea pigs were commonly used in scientific experiments because of their small size and ease of handling.
For example, if a new medication is being tested, the people who are given the medication for the first time are the "guinea pigs." They are the ones who are taking a risk by trying something that has not been fully tested yet.
The term can also be used more broadly to refer to someone who is being used as a test subject in any situation. For instance, if a friend is trying out a new recipe and asks you to taste it, you might jokingly say, "Am I your guinea pig?"
Overall, the idiom "guinea pig" is used to describe someone who is being used to test something new or unproven.
• The government's new policy is like using the entire country as a guinea pig in a grand experiment.
• I feel like a guinea pig in this new job. They keep changing my responsibilities and testing me in different areas.
• My little brother is a guinea pig for my grandma's new cookie recipe.
• The medical researchers are looking for volunteers to be guinea pigs for the new treatment.
• I don't want to be a guinea pig for the new software. I'll wait until it's been tested by others.
• The new teacher is using our class as guinea pigs to test out her innovative teaching methods.