What's in a synopsis?

Maybe this is too simple but,give them what they want. If one wants a short paragraph,do it. If one wants two pages,do it.I'd be encouraged to know that a synopsis was even wanted. Good luck.

The synopsis is there to show how the plot develops. With the query you can cheat and include a few interesting events that do not necessarily cover the whole book, or even not every aspect of the book. The synopsis is more precise (depending on length) but should include the major plot developments and ending.

Example:
Little Red Riding Hood query: "the coming-of-age story of a young girl, who has to overcome personal fears and find her inner strength to protect her family from a vicious predator."
Little Red Riding Hood synopsis: "Red Hood is sent through the woods to visit her grandma. On the way she encounters a scary wolf but manages to escape using her sharp wits. The wolf plots revenge and, knowing the woods well, manages to get to grandma's house where he impersonates grandma in order to trick Red Hood. But Red Hood is clever enough to resist the cunning predator. A friendly hunter helps Hood dispatch the wolf and free grandma."

A synopsis is the whole plot of your book, whether that be summarized to one page (a difficult task, but you should do it) or a 10-page overview (which almost no one wants, these days; you're more likely to be asked for one page).

The one-page synopsis can be single-spaced. Every other length of synopsis should be double-spaced (one blank line between each typed line, like in your manuscript). Never use less than 10pt font, and even then, you're reeeeally pushing it. The default is 12pt.

I find the best way to write a synopsis is to first go through the book and locate the "turning point" of each scene, i.e. the moment where things irrevocably change, whether that be due to someone's revelation, someone's action, an event occurring, etc. Your synopsis will consist of stringing all these turning points together and then smoothing the transitions so it makes coherent sense when read. If you need to make it shorter, you cut out the turning points for the subplots and summarize/gloss over things that are less important.

A couple of times over the years, an author named Gav Thrope has given his advice on how to write a synopsis. You can find his latest post on the subject, and a link to his earlier one, here - http://gavthorpe.co.uk/2015/10/21/synopsis-advice/

When I write a synopsis I first write a three or four or even five page version, then I go through and cut it down to two pages, then I go through and cut it down to one page. I save each version separately, because different people ask for different lengths of synopses. Starting long & cutting also helps me look at the whole picture & then figure out from there what's truly essential to understanding the plot.

What's in a synopsis? sweat, obsession, tears, hours and hours of work.
Usually a 1-2 page single spaced with space between paragraphs document showing your novel's story arc. They are difficult to write. Typically, character names are capitalized. You tell the ending.
Honestly, it's my least favorite part of querying. I seriously recommend reading synopses--Miss Snark's blog has some, many wiki pages for movies have one, this site's QLH.

Here is a great thread on the board: http://absolutewrite.com/forums/showthread.php?84990-How-to-Write-a-Synopsis
It's nicely detailed.