What does Blitzkreig mean in German?

Blitzkreig is German. What it means in English is lightning war, and the term "blitz" is applied to the bombings of various cities in Britain during the Second World War.

More technically, it was the coordinated invasion by aerial bombing and motorized infantry that conquered Poland in September, 1939, and France and Belgium in May, 1940. The sea invasion of Britain from across the Channel never materialized, in part due to the resources expended on the Eastern Front against the Soviet Union.