To attack or damage (a place) in a sudden and intense military campaign. The army planned to blitz the enemy's stronghold at dawn.
To conduct a fast and intensive effort or campaign in a non-military context. The company decided to blitz the market with their new product launch.
In American football, to rush the quarterback with more players than usual in an attempt to tackle or hurry him. The defense decided to blitz on third down to pressure the quarterback.