The Insititue of Electrical and Electronics Engineers (IEEE) (website) Standards Group for Verilog, known colloquially as the "VSG", was established in October of 1993 to standardize the Verilog language. The group released its first standard in December of 1995, known as IEEE 1364-1995.
The group release a revising of this standard in 2002, known as IEEE 1364-2001.
Significant publication errors marred this release, and hence the group got these fixed, and the document reprinted, as IEEE 1364-2001 Revision C.
The IEEE 1364 group is no longer active; its work has been taken over by the IEEE P1800 standards group, which is working on standardization of System Verilog as well as taking on maintenence ownership of IEEE 1364.
You can learn more about IEEE P1800 by sending email to firstname.lastname@example.org