The day commemorates the date when Christopher Columbus first set foot in the Americas.
Columbus’ voyages across the Atlantic Ocean initiated the European exploration and colonization of the Americas.
While the first voyage in 1492 was immensely significant, Columbus did not actually reach the American mainland until his 3rd voyage in 1498. Instead, while trying to find a sea route to India, he made landfall on an island in the Bahamas that he named San Salvador.
He was also not the earliest European explorer to reach the Americas.