A survivor is a minifig who didn't die in glorious battle. Don't worry, they will probably have a horrible and entertaining death later, but for now they are still alive.
Minifigs may survive a number of events: Zombie Apocalypses Genocides Nuclear Holocausts Assassinations Wars and Battles Natural Disasters Violent Trauma Serial Killers Cats
Depending on what they survived, they may pick up extra descriptions. For example, a minifig who survived the Zombie Apocalypse might be referred to as a Post-Apoc Survivor.