黑死病, also known as the Black Death, was a devastating pandemic that struck Europe in the 14th century. It is believed to have been caused by the bacterium Yersinia pestis, which was transmitted through fleas that infested rats. The disease led to the deaths of an estimated 25 million people, roughly one-third of Europe's population at the time. The outbreak began in 1347 and spread rapidly across the continent, causing widespread fear and social upheaval. Symptoms included fever, chills, and painful swellings called buboes. The Black Death had profound effects on European society, leading to changes in labor, economy, and public health practices.