A more thorough explanation:

Originalism is a way of interpreting legal texts, like the U.S. Constitution, that says we should understand them the way people did when they were written. This means we should look at what the people who wrote the text meant, and what people at the time understood it to mean. We can figure this out by looking at things like debates, dictionaries, and other legal documents from that time.

For example, if we were trying to understand what the Second Amendment to the U.S. Constitution means, an originalist would look at what people at the time thought it meant. They might look at debates from when the amendment was written, or at other laws from that time that used similar language. They would try to figure out what the people who wrote the amendment meant when they said "the right to bear arms."

Originalism is different from another way of interpreting legal texts called "living constitutionalism." Living constitutionalism says that the Constitution can change over time, and that we should interpret it in light of modern values and ideas. Originalism says that we should stick to the original meaning of the text, even if it doesn't match up with modern values.