"Dystopian" usually refers to some sort of fictional world where things are bad (a utopia gone wrong), often due to an oppressive government. So things like Blade Runner, Children of Men, Lois Lowry's The Giver, or George Orwell's 1984 count as dystopian literature. But we'd like to make an argument for including One Day here as well. Though it's a work of fiction, One Day is set in the very real gulag prison system of the Soviet Union. But the world within these prison camps is largely a created one: it's a world that totally inverts the normal, outside world. In the camps, social hierarchies are flipped upside down, illogical rules govern everyday life, and arbitrary, or unpredictable, punishments are the norm. As Shukhov himself notes at one point, the world of the camps turns people upside down and inside out (827). If that's not dystopian, we're not sure what is.
Next up we have historical fiction. Historical fiction basically means that the setting and events in the book are real but the characters are largely fictional. One Day definitely fits the bill here. The gulag labor camp is a real, historically accurate place, but Shukhov and his fellow inmates are all fictional characters. The events these men discuss, such as World War II, are all real, historical things as well.
Finally, we have realism. One Day is definitely a realist novel – nothing is sugarcoated or fantasy here. One Day uses highly detailed, and often harsh, language to really capture the actual, lived experience of being in a gulag. It's an unflinching report that has some things in common with a non-fiction newspaper article, in that it deals with a lot of facts and historically accurate details.