The term Normen, initially came from the Term "Norse men," an English term meaning "Men from the North." It became a blanket term for the Scandinavian tribes that today are called Vikings. As Viking settlements began to spread from Scandinavia across Northern Europe, and distinctions between different tribes were made, Norsemen was shortened to Nor-men, and became distinguished from the Danes and Saxons. Since the Nor-men always came across the English Channel, the French side of the Channel became known as Normandy. Today most Historians use Normen to refer to the Viking tribes settled in Normandy, most notably the followers of William the Conqueror.
The Normans were descendants of a group of Vikings who settled in France in the 9th century. They made their living by raiding other parts of France, until they were defeated in a battle by King Charles the Simple, who offered them the Duchy of Normandy if they would stop raiding and start protecting the coasts and rivers from other Vikings.
Eventually, Duke William II of Normandy managed to claim the throne of England, invade, and conquer the country. Other Normans took over parts of Ireland, Scotland, Italy, Sicily, and the Kingdom of Antioch.