Affidavit of Support.
Affidavit of support is known as sponsor in many part of the world. The Green card lottery instruction clearly state that all the greencard lottery winners must provided one affidavit of support through the I-134 form. The petitioner must be an American citizen or must be a LPR holder in the U.S.A. Also the petitioner must provide required relevant official papers to the greencard lottery winner.
On the day of their interview greencard lottery winners must provide these documents to the interviewing consular officer. This requirement will apply to the US visa lottery winners too when they want to change their current US status to the U.S LPR status, through USCIS office.
Affidavit of support must be provided through the I-134 form. While some consular offices want them in I-864 form from the green card lottery winners to issue the Immigrant visas. Some time the agreed petitioner may change his mind and don't want to support you, so there is no problem in changing with a new petitioner's name and information on the day of the green card lottery interview.
Those people, who don't have a petitioner to provide an affidavit of support for them, can proof that they have on arrival job arrangements and enough funds to meet their needs in the USA. In this case, the consular officer will decide on whether to issue the required immigrant visa for the green card lottery winner or reject the visas.