juneteenth

From PBS.ORG:

The U.S. government is catching up with Black people who have been commemorating the end of slavery in the United States for generations with a day called “Juneteenth.”

President Joe Biden signed a bill Thursday that was passed by Congress to set aside Juneteenth, or June 19th, as a federal holiday. “I hope this is the beginning of a change in the way we deal with one another,” he said.

The Senate approved the bill unanimously; only 14 House Republicans — many representing states that were part of the slave-holding Confederacy in the 19th century — opposed the measure.

What is this federal holiday, and what is its history?