An unconditioned behavior is not brought about by learning. Sneezing is an unconditioned behavior. Unconditioned also means without conditions, as in unconditioned love, which is love that will always be, even if your mate starts wearing socks with sandals.
There are two sense of unconditioned, but they both involve things that happen regardless of outside events. An unconditioned behavior is innate — babies aren't taught (or conditioned) to cry, so that behavior is unconditioned. Other uses of unconditioned mean that something has no conditions and could last forever, like unconditioned peace, or even an unconditioned agreement that will be honored in any circumstances. No conditions can stop it.