What is meant by preference category for a family based Green Card?
Foreign nationals who want to become United States immigrants are classified into categories based on a preference system. If you are the parent, spouse or unmarried child under the age of 21 of a U.S. citizen, you do not have to wait for an immigrant visa number to become available once the visa petition filed for you is approved by the United States Citizenship and Immigration Services (USCIS). An immigrant visa number will be immediately available for you. The relatives in the remaining categories must wait for an immigrant visa number to become available according to certain preferences.