Segregation means keeping things or people apart. In United States history, it means the laws and customs that kept black people separate from white people. By 1804, all the northern states in the U.S. had ended slavery. It took the Civil War and the 13th Amendment to legally end slavery all over the United States. Segregation, however, lasted a lot longer.
After slavery ended in the U.S., groups of laws were passed to keep black people away from white people. They kept black people out of white schools, theaters, parks, pools, and neighborhoods. There were even separate cemeteries and jails for black people.