Short answers, pulled from the story.
Normandy takes its name from the Viking Northmen who settled the territory starting in the 9th century. The name was confirmed by the Treaty of Saint-Clair-sur-Epte in 911, when the Viking leader Rollo entered vassalage to the king of West Francia and received land around the lower Seine.
The Treaty of Saint-Clair-sur-Epte was a 911 agreement between King Charles the Simple of West Francia and the Viking leader Rollo. It granted Rollo and his followers territory centered on Rouen in exchange for conversion to Christianity, homage to the king, and an obligation to defend the coast against further Viking attacks, creating the foundation of the Duchy of Normandy.
The D-Day landings took place on the 6th of June 1944, under the code name Operation Overlord. The Allied invasion targeted Normandy's beaches, and the Battle of Normandy continued until the closing of the Falaise gap between Chambois and Mont Ormel, after which Le Havre was liberated.
The Channel Islands are historically part of Normandy but are now British Crown Dependencies, not part of France. They cover 194 km2 and comprise two bailiwicks, Guernsey and Jersey. The British monarch is still informally referred to in the Channel Islands by the title Duke of Normandy, and the loyal toast there is Le Roi, notre Duc.
Normandy is known for cheeses including Camembert, Livarot, Pont l'Évêque, and Neufchâtel, as well as calvados (apple brandy), cider, and pommeau. It is the chief oyster-cultivating, scallop-exporting, and mussel-raising region in France. The mealtime custom called the trou normand, a glass of calvados taken between courses, is a regional tradition still observed in many homes and restaurants.
Rollo, known in Old Norse as Hrólfr, was the Viking leader who received the territory around the lower Seine from King Charles the Simple in 911 through the Treaty of Saint-Clair-sur-Epte, founding the Duchy of Normandy. His descendant William became king of England in 1066 after defeating Harold Godwinson at the Battle of Hastings, while retaining the fiefdom of Normandy.