Why are American movies called "blockbusters"?

As the name implies, blockbusters are "big" movies with big directors, big stars, big productions, big investments, big scenes, big lineups, big returns and so on. Such as the familiar Titanic. The director is James Cameron. James Cameron; Actors Leonardo DiCaprio/Kate Winslet/kathy bates/gloria stuart; Won 1 1 awards for best film, best director, best sound effect and best photography in the 69th Oscar. Titanic's global box office revenue was $654.38+08 billion, of which North America earned $600 million, ranking first in the history of the world and North America, and its record has never been surpassed. It is the highest-grossing documentary in the current film history and the most Oscar-winning film.