Short answers, pulled from the story.
The Black Death was a plague pandemic that occurred in Europe from 1346 to 1353. It killed as many as 50 million people, perhaps 50 percent of Europe's 14th-century population, making it one of the most fatal pandemics in human history.
The Black Death was caused by the bacterium Yersinia pestis, spread by fleas and through the air. The bacterium was discovered by Alexandre Yersin during an epidemic of bubonic plague in Hong Kong in 1894.
Genetic evidence points to a Central Asian origin, with the earliest known victims found at the Kara-Djigach and Burana cemeteries near Lake Issyk-Kul in modern Kyrgyzstan, where tombstones recorded a spike in deaths from pestilence in 1338 to 1339. This strain was the direct ancestor of the strains that struck Europe starting in 1346 to 1347, though the exact territorial origin remains disputed.
The Black Death was reportedly first introduced to Europe during the siege of the Genoese port of Caffa in Crimea, where the Golden Horde army of Jani Beg catapulted plague-infected corpses over the city walls. Genoese traders then fled to Constantinople, where the disease first arrived in Europe in the summer of 1347, before spreading by ship to Sicily, Italy, and the rest of the continent.
The most commonly noted symptom was the appearance of buboes in the groin, neck, and armpits, which oozed pus and bled when opened, accompanied by fever of 38 to 41 degrees Celsius, headaches, aching joints, nausea, and vomiting. Three forms existed: bubonic plague killed 80 percent of untreated victims within eight days, pneumonic plague had a mortality rate of 90 to 95 percent, and septicemic plague had an untreated mortality rate near 100 percent.
The term Black Death was not used for this pandemic until the 1750s and is first attested in 1755, where it translated the Danish den sorte dod. At the time of the 1347 outbreak, no European language called the plague black; contemporary writers used Latin terms like pestis, pestilentia, and mortalitas.
Wages soared in response to a labour shortage, rents collapsed, and many survivors inherited property, which contributed to the destabilization of feudalism. The pandemic also triggered persecutions, including the Strasbourg massacre of February 1349 in which about 2,000 Jews were murdered, and gave rise to the practice of quarantine, first imposed as a thirty-day isolation in Ragusa in 1377.