An elevator pitch is basically your ability to pitch a book in 1 or 2 lines. So…for example, let’s take a look at some classics most people know.
Harry Potter & the Goblet of Fire: Four wizards compete in a three-wizard tournament. Scandal! (I borrowed that from @polandbananas20).
The Hobbit: middle-aged introvert dragged along by dwarves who want to slay a dragon and get their kingdom back.
Throne of Glass: Game of Thrones meets The Hunger Games with really pretty dresses.
Delirium: Romeo & Juliet in a dystopian world where love is considered to be a mental illness.
Great (by Sara J. Benincasa): an adaptation of The Great Gatsby in modern day except with lesbians.
The Selection: The Bachelor, royal edition, with mild civil war (also borrowed/paraphrased from @polandbananas20)
So like, if I wanted to do elevator pitches for some of my books, I might write them something like this:
Eidolon: Edgar Allan Poe meets Batman when Jack the Ripper stalks a neo-Victorian kingdom of half-human magicians.
The Silver Princess: royal Elf twins fall in love with a young doctor while their nations teeter on the brink of civil war.
Frost & Fire: a vindictive brother and sister try to ruin the lives of their fellow students at magic school.
Make sense?