Fallout is a series of post-apocalyptic science fiction role-playing video games, set in an alternate timeline in which the Cold War paranoia of the 1950s continued into the 2070s. Technology advanced rapidly, leading to overconsumption of resources, leading further to massive wars over fuel supplies. Large nuclear shelter cities - called Vaults - were constructed to shield their inhabitants from the incoming worldwide nuclear war... which finally happened on October 23rd, 2077, bringing civilization to ruins.
Decades later, as the radiation died down, the vault dwellers emerged from their shelter cities and began to build new civilizations in the ashes of the Old World. War, pain, and hilarity ensue. The games feature action-survival gameplay, with the stories generally being a mix of social commentary, satire, and an eclectic sense of humor, typically (though not always) dealing with the adventures of various Vault Dwellers.