The term "sponsor" usually means to "petition for" permanent resident status on behalf of a foreign citizen. The sponsor may be a family member who is a U.S. citizen or permanent resident, a U.S. employer or an American seeking to adopt an overseas orphan.
Another meaning of the term "sponsor" is a person who completes Form I-864, Affidavit of Support under Section 213A of the Act as part of a family petition. By signing the form, the sponsor agrees to provide the sponsored immigrant(s) whatever support is necessary to maintain them at an income that is at least 125 percent of the Federal poverty income guidelines" until the contract terminates. The contract terminates when the alien becomes a US citizen or has 40 quarters paid into the Social Security system.