It's an immigration program that's been around for more than two decades, offering a limited number of visas to people from across the world.
Well known abroad, it has received little public attention in the U.S. _ until now.
On Wednesday _ a day after a rented pickup barreled down a crowded bicycle path in Manhattan, killing eight people _ federal officials said the suspect in the attack, 29-year-old Sayfullo Saipov, had entered the country from Uzbekistan in 2010 through the Diversity Immigrant Visa program.
That kicked off a political debate.
"He came in through the diversity program ... we're going to stop that," President Donald Trump told reporters.
Here is some background on the program best known as the "visa lottery."
