A more thorough explanation:

Korematsu v. United States was a case that went to the U.S. Supreme Court during World War II. The case was about whether it was okay for the government to force Japanese Americans to leave their homes and live in internment camps during the war.

The Supreme Court decided that it was constitutional for the government to exclude all people of Japanese ancestry from certain military areas. However, the Court also said that any law that takes away the civil rights of a single racial group should be looked at very carefully to make sure it's fair. The Court said that forcing large groups of citizens to leave their homes is not okay unless there is a direct emergency.

For example, if there was a big fire in a neighborhood and the police told everyone to leave their homes for their safety, that would be a direct emergency. But if the government just decided to make a law that said all people of a certain race had to leave their homes for no reason, that would not be okay.