Synopsis/Summary?

I'm not an expert, but here's how I differentiate them:

Summary -- One to three paragraphs, as part of a query letter, that describe your book in such a manner that it leaves the reader wanting more. It follows a basic premise of introducing the hero, the villain, the stakes, and the consequences if those stakes aren't met. The ending is not told.

Synopsis -- Can range from one to ten pages (or longer, depending on what the agent requests). It supplies a thorough description of the action, including major characters, turning points, plot twists, and the ending is revealed.

I pretty much agree with ChaosTitan.

What's annoying about it, though, is that in other contexts, when someone says "summarize it for me" they want to know everything, including the ending. So the word has a double meaning, I think

Yup, a summary is kind of like your elevator pitch -- tell me what your story is about and hook me within a few sentence.

A synopsis must have a beginning, middle and ending.