The Diversity Immigrant Visa program, also known as the green card lottery, is a United States congressionally mandated lottery program for receiving a United States Permanent Resident Card. The Immigration Act of 1990 established the current and permanent Diversity Visa (DV) program.
The lottery is administered by the Department of State and conducted under the Immigration and Nationality Act (INA) as amended by the Immigration Act of 1990. The lottery makes available 50,000 permanent resident visas annually and aims to diversify the immigrant population in the United States, by selecting applicants from countries with low rates of immigration in the five years prior.
The program received widespread attention after eight people were killed in a terrorist attack by a recipient of a Diversity Immigrant Visa. Wikipedia