If you look a few sections above in 17 U.S. Code § 101 which contains the definitions applicable to the copyright code "work of the United States Government" is

If you look a few sections above in 17 U.S. Code § 101 which contains the definitions applicable to the copyright code "work of the United States Government" is defined. > A “work of the United States Government” is a work prepared by an officer or employee of the United States Government as part of that person’s official duties.