Quarantine means a period of isolation in which people that may have been exposed to infectious or contagious disease are separated from the general population. Quarantine, or self-isolation, is a very effective way to prevent further spread of a disease.
While quarantine means isolation for 40 days in Italian, modern quarantine often is only as long as the incubation period of a disease. In the case of COVID-19, after exposure most people will exhibit symptoms of the disease within 14 days. Receiving doctor’s orders or self-isolating because you have COVID-19 or were exposed to it usually only last 2 weeks.
If someone in quarantine did not get sick during the 14 days, they are not not considered a risk for spreading it further if they contracted it without symptoms. If they did exhibit symptoms in quarantine and recovered, they are also not considered a risk for spreading it further.