A condensed summary of the full story - including the ending - for readers, contests, and queries.
A synopsis tells the whole story in a page or so, ending included - its job is to prove the story holds together, not to tease. Coverage readers write one to demonstrate comprehension; writers submit one wherever a stranger must judge the story before reading it all.
If a synopsis is hard to write, mine that difficulty: the passages that resist summary are usually where the plot's logic is soft.