Strictly speaking, the Defender is the yacht club that holds the America’s Cup, at present the Golden Gate YC (GGYC), also referred to as the Trustee. Oracle Team USA is GGYC’s representative in the racing. “Defender” is also the term for the yacht that sails in the America’s Cup Match against the Challenger.
Golden Gate YC manages America’s Cup issues, per an agreement with Oracle Team USA, via a five-person committee of GGYC members, three of whom are also team members of Oracle. Rights and responsibilities of the Trustee/Defender are addressed in the Protocol, but the basis for the roles of the Defender and Challenger stems from the Deed of Gift.