|The Simple English Wiktionary has a definition for: summary.|
A summary is a condensed explanation of an event, story, document, etc.. i.e. "summing up the facts." They are not constrained to any medium or topics. Not to be confused with abstract, which is a summary of a document. There are many different levels of summarization that can be done. The summarizer may choose any length, but the sumarees may not appreciate anything more than absolutely necessary to get the required facts.
Summaries help to spread information fast. They also help people make decisions on if it is something worth looking further into.
A quick "good/bad" can suffice in some situations. In other situations, the summary may rival the length of the original.
"This book was really cool. This guy drives a pickup to work everyday, and has a dangerous job."