In Infinite Jest, O.N.A.N. is the Organization of North American Nations, which includes the United States, Canada, and Mexico.
Onanism is defined by the OED as "Masturbation. Also: coitus interruptus." The term is derived from Genesis 38:8-10.
Frank Louis Cioffi writes: “Not surprisingly, in the world of the novel, the U.S. has been renamed O.N.A.N., an acronym suggesting the self-absorbed disconnection and solitary pleasure-seeking of its citizenry” (Coiffi 172).