Ugh! Every writer's nightmare...
You spend perhaps years planning, researching, writing, re-writing, editing, proofreading, and everything else that goes into the creation of a novel; and some donk comes along and wants you to summarise it in a soundbite! "None of your business!" you shout as you run back into the bushes of imposter syndrome. (Yes, yes, I know it's probably the most used meme out there!)
Let me assure you that the path to peace has a slight diversion in it, and one that you might consider - if, indeed, this bothers you at all. But for those of you who are loath to distill years of work into a 30-second explainer, here is my advice on how to answer the question, "What is your book about?"
Firstly, don't panic. Now ask yourself this question - what do they mean by 'about'? Aha, I've got you now! Your little brains are thinking, "What does he mean by 'what do they mean'?"
Well, it's like this: in genre fiction, many writers imbue their stories with subtext and 'the real meaning' underlying their tale. I'm sure this makes immediate sense to you. Fictional societies and social structures, religious and political organisations; dogmas and legislation; characters and groups with shared ethnic, racial and physical traits - all these things and more are designed to be metaphorical, allegorical, analogous, representative of something you humans experience in your everyday lives or across your societies as a whole. Like a deskbound activist, you structure ways to comment on the ills of the world, grinning maniacally in your self-righteous certainty that "this'll show 'em".
Now, this may not be your intention, and indeed you may not even believe it to be true of your work; but more often than not, you humans subconsciously infuse your work with inspiration from the real world, past or present. I would suggest that your work is always reflective of your interests and concerns, intended or not; and herein lies the answer to the question, "What is your book about?"
The problem with expressing this, however - even if it's something that will only result from some soul-searching about your purpose in writing your book - is that you might give away the plot in line with the purpose. What a book is 'about' is often not revealed until the latter parts of it; and if you're writing a trilogy or series, for example, there's no way you want to give away any of this in the early stages - if at all!
"So, oh great and terrible Gatekeeper," I hear you ask, "bestow your wisdom upon us. How do we navigate these tumultuous waters?"
Well, I'm glad you asked. That was you, right? I'm worried the voices might be back. I usually ignore them and keep on killing...er...where was I?...oh yes!
You see, when people ask what your book is about, that's not really what they're asking. In essence, responding with 'the terrors of war' or 'the psychological trauma of displacement' or 'the inherent corruption of modern capitalism' is likely to turn people off reading your work. And yet that's what the book is about, at its core - that's its subtext, its 'intrinsic' meaning. What the hell do these people want?
All they really want - and all you need to give them - is a reason to be interested in your work; and while the reason you provide might be different depending on the person asking (you can play a different 'angle' with everyone; just don't play an angel - you'll always lose), you should grab them by the shoulders and shove them down the path I mentioned earlier - the diversion. Because all they want to know is what happens in your book. And not even throughout the whole thing - just the core of it, or perhaps just the start of it. What is the hook? What is the obstacle? What trials will our heroes face? What dangers lie in store for the intrepid reader? It doesn't matter what it's 'about' - not yet anyway; but it matters what happens. That's the question they're asking.
And yet a problem remains. Amidst the complexity of your plot - because, let's face it, no one fights a monster for 100,000 words - the compulsion is to launch into a passionate rant about the story. There you are, frothing from the mouth, spittle flying, someone's passing around safety goggles and COVID wipes, and you're only one chapter in...! What madness is this?
So...rewind. Compose yourself. Wonder aloud where that freak rain shower came from. Enjoy their confusion. Deep breath, and...proceed.
Proceed to introduce them to your protagonist, perhaps, or your group or species or society who will face the challenges you've laid out in your story. Be aware of cliches - of course, it's genre fiction, so they're everywhere, but you must have a new spin, something different - and deliver a setup within a context within a theme; a trial within a challenge; a danger within a horror. The less complexity the better - no more than two or three layers, perhaps. Something happens to someone and they have to deal with it in the face of this other thing. Can it come down to that?
That, my dear human scribe, is up to you.