One of the bigger parts of writing non-fiction is the 'query'. Functionally, its a short description of your novel that's designed to explain what you're writing - a synopsis, if you will. If you imagine it as the brief blurb on the back of a book, you'd be on the right track. Unfortunately, the reality is much sloppier.
Queries have become these weird monstrosities that combine the worst features of fan mail with a ton of unwritten rules and secret handshakes, and their acceptance is at the whim of the agent or editor reading it. There's quite a few websites out there dedicated to dissecting a query with an Asperger's like focus on diagramming everything. However, this means absolutely nothing. The individual gatekeepers in this industry refuse to set down a standard, and instead judge quite a bit by their 'gut', which more and more is coming to mean "Do I know you from the Buffyverse forum I post on?"
Queryshark is a popular website run by a 'leading agent in the industry' who has a really bad habit of doing this kind of irregular shit. In one post she'll complain bitterly about how even though this one followed all of her rules, its just not interesting. However in the next post she'll rave about how this one broke all of her rules, and she loves it. There are no standards, just a lot of fucking 'gut feelings' that can come or go at a whim.
This is another issue with the female dominated writing industry, where social media connections and re-tweeting people count for more than the actual product you have. There's also the strong conformist element with many agents and editors, which is why you've got Young Adult pushing the same shit in waves. At one point, mermaids were the Next Big Thing, and if you had a mermaid Young Adult novel ready to go, you were set. Doesn't matter worth a fuck that they all had the same plot (I'm a magical princess but I'm in love with a broody landlubber!), its what people want!