Juneteenth is a national day of celebration memorializing the end of slavery in the United States. It was in 1865, on June 19th, that enslaved black people in Texas learned that the Civil War had ended and that they were free, more than two years after the effective date of the Emancipation Proclamation.
For more information on Juneteenth, see https://www.history.com/news/what-is-juneteenth.