The US Code, which is the law (including the regulations) created by the Immigration and Naturalization Service (INS), sets forth the definition of Immediate Relatives:

• Spouse of a US Citizen;
• Unmarried child, under the age of 21, of a US citizen;
• Parent of a US citizen; or
• Spouse of a deceased US citizen [some exceptions.]

As an Immediate Relative, there are no quotas that the government sets forth as to the number of Green Cards for which one can apply. Instead, the government will allow any bona fide immigrant who is classified as an Immediate Relative to be issued a Green Card, usually without delay. In effect, if you are an Immediate Relative as defined, there is "little doubt" that you will be issued a Green Card, although, as with all United States laws and regulations, there are exceptions and unclear situations.