Not specifically publisher speak, so this is a bit of rogue entry. 'Boring bits' is not jargon for anything - it means the bits of your book that are boring in plain, ordinary English.
Some bits of a book are boring to write. On the whole, they are also boring to read. The obvious solution is not to write them so no one will have to read them. Is that a realistic ambition? Let's step back. What counts as boring?
Personally, I would always skip the Elvish claptrap and the doggerel verses in Lord of the Rings (LotR is not my preferred reading anyway, but I read it aloud to Big Bint over a period of 18 months). These are definitely boring bits. I skip some of the war in War and Peace. And I skip anything that goes into detail about vehicles or other mechanical stuff in anything - just not interested. But of course there are people who really like reading about war and vehicles, and possibly even Elvish claptrap, so they would think I'm skipping the best bits. No request for Tolstoy or Tolkien to miss these out - they're just not to my taste. It's my fault as a reader if I pick books I'm not interested in; that's not the same as the book being boring or having boring bits per se.
But in other books there are boring bits that anyone would find boring. In a non-fiction book, it might be setting out the basic rather dull info you need in order to understand the really exciting bit that will only make sense if it's built on a solid foundation. In a story/novel, you might need to move characters plausibly from one place to another, kick-start a train of events that will lead to a crisis, or add some form of explanation so that readers continue to believe in what's happening.
Here's an example. I currently have to get my heroine, a vampire who models for Jack Wills, from her home with her neurotic, controlling mother to a photo-shoot during which she will be guillotined by a rival during a mock-up of the French Revolution. That is not, I think, a boring premise for an episode. But she has to be invited to the shoot, persuade her mother to let her go, get there, do some non-threatening photos and so on before the exciting bit can happen. How long will the reader stay with me? I'm already thinking 'I don't want to write this bit, it's boring'.
Of course, as the writer you can skip ahead and write the exciting bit first, but how to stop the reader skipping ahead? There are conflicting demands here: the integrity and plausibility of the story depend on setting up the incident, but the readers need to be drawn through the less exciting parts or they won't even get to the 'good bit'. The answer, of course, is to stop the boring bits being boring. To do this, you need to insert lots of micro-narrative elements. In this example, it could be an argument with the mother in which it looks as though the girl won't get to the shoot. We have to want her to go, be on her side and keep reading. And I have to sneak info into this argument that moves the story forwards. In a non-fiction book, it requires showing why or how the foundation information is interesting. And that means creating wonder - an underrated commodity that needs a post of its own.
If your publisher thinks your book has boring bits, they will (if you're lucky) ask you to rewrite to remove them. What they really mean is remove the boring, not necessarily remove the bits - though you do need to check that the bits are actually essential and not just an indulgence (because you really like describing horses, for example). If you're unlucky, they'll just reject the book. It all depends on the ratio of boring:exciting.
If boring has an interest level of 0 and crisis has an interest level of 100, your book (of any type) must have no bits with a score of 0 and the rest going in a series of peaks with at least one getting to 100. Too intense for too long and it loses impact, but too long a stretch without anything exciting happening and it loses readers. The exact balance depends on the type of book/readers, but as a general rule if you find it boring to write, readers will find it boring to read. Don't go there. Add some excitement.
I might make an exception to that rule about vehicles - a tumbril can be exciting. When you think it's a two-wheeled cart, it doesn't look very interesting but once you know it's carrying a disgraced aristocrat to the guillotine, it gets a whole lot more engaging. Fill your writing with well-loaded tumbrils and expunge the carts.