The Blitz was the bombing of Britain by Nazi Germany between September 1940 and May 1941. It was a very important part of the Second World War.
The German airforce, called the Luftwaffe, used bombs to damage industrial areas like factories and docks. That meant it was hard for Britain to make and move things like the weapons that were needed to fight the Nazi's.
They also attacked civilian areas, the parts of cities where people lived. Thousands of people died after weeks of raids. The Nazis were planning to invade Britain. They wanted to make ordinary people in the UK feel that Britain couldn't win - so that the British would put up less of a fight. They thought that would happen if they'd seen ordinary people killed and their homes and cities destroyed.
The German planes flew over to the UK in big groups for bombing raids. They dropped lots of bombs in a short amount of time, making it a terrifying experience for the people on the ground. In September 1940, the Luftwaffe dropped 5,300 tons of high explosives on London in just 24 nights.
Blitz is a German word for lightning, it was used by British Newspapers to describe the heavy and repeated bombing raids.
No, the Blitz also happened in other cities. The first big raid on London was in Sept 1940, but after that the German planes hit other targets like big ports and places with lots of factories.
In November 1940, 500 German bombers dropped 500 tons of explosives and nearly 900 incendiary fire-bombs on the city of Coventry. All the bombs fell in a 10 hour raid and many areas were completely destroyed.
After May 1941 the bombing raids on British cities were reduced, this was because the Germans wanted to use more of their forces to attack Russia. But the bombing didn't stop, raids carried on for several more years.