The term "Boilerplate" goes back to my old stomping grounds in Chicago. The American Press Association shared a building with a metal plant that rolled sheet metal into boilers. The APA had its pressing running all day, churning out syndicated content in what the printers jokingly referred to as their own "boilerplate factory". Just like the identical boilers coming off the metalworkers' assembly line, the syndicated content was the same in every publication it appeared in, and was often little more than filler.
Boilerplate code is code that's the same in every program. It's the initialization routines or basic class structure you either copy & paste into every project or have generated for you. It needs to be there for everything to run, but you didn't code it and it doesn't mean anything in the context of your project.
A good, basic example is how every C program has a main function: int main(int argc, char** argv). It's not unique to your program‚ and it doesn't reflect what your code actually does. But it needs to be there or else C doesn't know where to start your program or what value to return to the operating system.