The plague is generally considered to be a result of infection by the bacteria Yersinia pestis, and was transmitted via a rat vector?, although other infectious agents have been suggested.
The disease is known as "bubonic" plague after the "buboes" or swellings that are characteristic of infection. The plague was also known as the "Black Death" at the time of its most virulent outbreak in Europe in 1347-53.
The 1665 epidemic was in fact on a far smaller scale, but was remembered afterwards as the "great" plague because it was one of the last widespread outbreaks in Europe.
This particular incidence of the disease sometimes claimed to be commemorated in the childrens' nursery rhyme "Ring of roses":
"A ring-a-ring of roses,
A pocket full of posies,
A tishoo, a tishoo,
We all fall down"
The ring of roses was the characteristic formation of buboes in the early stage of infections. The posies were flowers thought to ward off infection. The third line refers to sneezing, which was another early symptom. The last line refers to be dying which is what commonly happened next.
A variant of the rhyme is:
"Ring around the rosies
Pocket full of posies
Ashes, ashes
We all fall down"
However, this theory about this rhyme is nothing more than speculation: the rhyme was first published in 1881. A good summary of the argument against this theory may be found at http://www.snopes2.com/language/literary/rosie.htm.
After a localised outbreak in Provence in southern France in 1720-21, Europe suffered no more such atacks of plague, though the disease remained virulent in other regions, killing over a million in India in the first quarter of the twentieth century.