Short answers, pulled from the story.
The International Astronomical Union currently recognizes 9,137 lunar craters, of which 1,675 have been dated. In addition, at least 1.3 million craters larger than 1 km in diameter exist on the Moon's surface.
Evidence from the Apollo Project and uncrewed spacecraft proved conclusively that almost all lunar craters were formed by meteoric or asteroid impacts. Smaller craters result from meteoric impacts, while larger ones were caused by asteroid strikes.
Galileo first observed the Moon's cup-like depressions on the 30th of November 1609, after building his telescope in late 1609. The term "craters" was not applied to these features until Johann Hieronymus Schröter named them in 1791.
Chuck Wood and Leif Andersson of the Lunar and Planetary Lab devised a classification system for lunar impact craters in 1978. Their five-category system, known as LPC Crater Types, accounts for about 99% of all lunar impact craters.
Craters constitute 95% of all named lunar features and are usually named after deceased scientists and explorers, a tradition started by Giovanni Battista Riccioli in 1651. Since 1919, the International Astronomical Union regulates the assignment of these names.
The largest crater described as such is approximately 290 km across in diameter and is located near the lunar south pole. Beyond a couple of hundred kilometers in diameter, craters are generally classified as basins rather than craters.