SO is the acronym for 'Supporting Organizationsand represents the advisory bodies the ICANN (Internet Corporation for Assigned Names and Numbers) Board, with a primary responsibility of developing and recommending substantive policies regarding those matters falling within their specific responsibilities.
The SOs are three specialized advisory bodies that have the purpose of advising ICANN Board of Directors related to issues regarding domain names and IP addresses. ICANN's supporting organizations are also referred to as "SOs". Currently, there are three main SOs. For advisory related to domain names the main advisory bodies of ICANN are GNSO (Generic Names Supporting Organization) which deals with policy making for gTLDand CCNSO (Country Code Names Supporting Organization) which deals with policy making for ccTLD, while in the case of IP addresses the main advisory body is represented by ASO (Address Supporting Organization) which deals with policy making for IP addresses.
Apart from these supporting organizations, ICANNalso relies on the advisory committees for advice regarding the interests of their stakeholders which are not part of any SOs.
ICANN outlines three supporting organizations, of which the GNSO belongs. The main objective of SOs is to help the promotion for Internet policy development and encourages diverse international participation related to the Internet's technical management. Each SO names two Directors to the ICANN Board.
The Generic Names Supporting Organization develops policies for generic Top-Level Domains and it makes struggles to operate in a fair, orderly manner throughout the global Internet, while promoting innovation and competition. The GNSO deals with issues related to registration of a domain name, the services which must be provided by a registrar and even cases related with the renewal of a domain name.
The Generic Names Supporting Organization (GNSO) of ICANN is the successor of the Domain Name Supporting Organization(DNSO). ICANN outlines three supporting organizations, of which the GNSO belongs.
The Country Code Names Supporting Organization is a body of ICANN created specifically for ccTLD managers. Along with GNSO and ASO it provides advice for ICANN Board of Directors related to issues regarding domain names. It was created in 2003 and has also developed a forum for ccTLD managers where they can meet and discuss various topic of interest, but it encourages technical cooperation for ccTLd managers. The CCNSO is also responsible for developing ICANN global policies for issues related to ccTLD. 
The Address Supporting Organization (ASO) is one of the supporting organizations of ICANN which according to the ByLaws should be “formed through community consensus”. The main objective and purpose of ASO is to review and develop recommendations related to address policies of IP (Internet Protocol) to advise the ICANN Board.