Somebody has enquired as to what block it is precisely that a blockbuster film busts.
Well, I assume that she meant film. But a blockbuster was originally a kind of bomb. The phrase dates from 1942 when the large bombs of more than eight thousand pounds began to be referred to as blockbusters. But of course, that's explosives and not films.
The second well-attested meaning of blockbuster is rather stranger. It's a kind of estate agent. Specifically, it was a kind of American real estate agent who would irritate the hell out of white people by selling one house on the block to a black person, which apparently in 1950s and 60s America was somewhat controversial.
But the films? Nobody is quite sure. There are two theories. The first is that it's a simple transfer of the explosive power of the blockbusting bomb. There's a line in a detective novel from 1957 that goes:
One day I had what seemed to me like a block~buster of an idea for a musical play.
However, the term didn't really catch on until the 1970s when spectacular and super-grosser were pushed out of the lexicon and blockbuster took their place.
The other theory is just that: a theory. It may well not be true but showbiz folklore says that a blockbuster is a show that is so popular that all the other theatres on the block are bankrupted, and end up bust. This doesn't really work as, presumably, they would profit from the ticketless turnaways who couldn't get into the main show.
This amuses me.