A blockbuster is a Hollywood movie that's made with a large budget and big stars. A true blockbuster is extremely popular and brings in a lot of money.
Typically, a blockbuster is a fabulous summer movie that audiences line up to see the first weekend it's released. You can also call a successful play or a new, popular video game a blockbuster. Less, often, a huge bomb is a blockbuster — this is the word's original, 1940s meaning, from the fact that such a bomb could destroy an entire city block. The entertainment meaning, from the 1950s, began as theater slang.