Blockbuster or "cookie" was the name given to several of the largest conventional bomb

Bomb

A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

s used in World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 by the Royal Air Force

Royal Air Force

The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 (RAF). The term Blockbuster was originally a name coined by the press and referred to a bomb which had enough explosive power to destroy an entire city block

City block

A city block, urban block or simply block is a central element of urban planning and urban design. A city block is the smallest area that is surrounded by streets. City blocks are the space for buildings within the street pattern of a city, they form the basic unit of a city's urban fabric...

.
The bombs then called Blockbusters were the RAF's 4,000 lb — also known as a cookie — 8,000 and 12,000 lb (1,800, 3,600 and 5,400 kg) HC (High Capacity) bombs.