A snow job is what happens when someone misrepresents something that happened. If you convince your brother that your dad ate the last of the ice cream, but you're actually the guilty one, that's a snow job.
If you tell a long, elaborate lie, especially one that's meant to hide evidence of some mistake or crime, you're pulling a snow job. This informal North American term is simply another way to say "cover-up" or "misrepresentation." Most of the wrongdoing that happened during the Watergate scandal of the 1970s involved the snow job that followed the initial crimes. Snow job comes from World War II army slang.