So this is meant to answer the question, "What is your book about?"
When soliciting an agent to sell your book to a publisher, there is something you must write called a query letter. You also have to be able to summarize your book in a few paragraphs. Here's a few things I wrote this morning towards that end. Not a query letter, just some early attempts to come up with some language to describe the book. Of course If I were writing this for a proposal or query letter it would need some seriously editing.
My book isn't too terribly high concept so I have no fear of anyone absconding with my great idea. This is the basic premise:
Horses are a popular subject among girls, but most novels about horses are written for younger readers. I Dig a Pony is a book about horses for older girls reminiscent of the books they may have read when they were younger but written from a more mature, contemporary perspective. To get an idea of the tone of I Dig a Pony, imagine Misty of Chincoteague if it were written in the style of Rachel Cohn.
This might be something I would write in the opening of my Query letter: some reason why someone would want to publish my book and some indication that it resembles other contemporary fiction in the genre. Rachel Cohn wrote Nick and Norah's Infinite Playlist which, although nothing at all like the book I wrote, is written in contemporary language for the same age group that I'm going for. Cohn is hot stuff right now due to the recent popular movie based on her book, so I thought mentioning her would demonstrate that I know something about the present condition of young adult fiction.
Edit: My synopsis of this book was premature. I'm still working out the kinks.