A blitzkrieg is an intense and brutal military campaign. If you're studying the history of World War II, you'll eventually come across the word blitzkrieg.
The noun blitzkrieg means a very quick, particularly violent and intimidating attack by one armed force against an enemy, but it almost always refers specifically to the German military offensive during World War II. The word blitzkrieg means "rapid attack" in German, from blitz, or "lightning," paired with krieg, or "war." The blitzkrieg waged by Germany on England in 1940 and 1941 is often referred to as "the Blitz."