A quarantine is used to separate and restrict the movement of persons; it is a 'state of enforced isolation'. This is often used in connection to disease and illness, such as those who may possibly have been exposed to a communicable disease. The term is often erroneously used to mean medical isolation, which is "to separate ill persons who have a communicable disease from those who are healthy." The word comes from the Italian (seventeenth-century Venetian) quaranta, meaning forty, which is the number of days ships were required to be isolated before passengers and crew could go ashore during the Black Death plague epidemic. Quarantine can be applied to humans, but also to animals of various kinds, and both as part of border control as well as within a country.