Search engines shows snippets next to each search results so you can decide if a page is relevant without visiting it first. But snippets are pretty short and focus on the text that includes your keywords. To find more about a page, a text summarizer that shows the key phrases would be helpful.
Syntatica is a company that combined search results with summarization and the results is Syntatica Search. If you leave behind the fact that Syntatica uses Live Search, you'll notice that the summary gives you a better idea about the content of a page than the snippet. This works well especially with pages that have a lot of content on a single topic.
"Unlike conventional search-and-retrieval programs, Syntactica does not simply match strings of letters to other strings of letters in an index. It analyzes concepts in the context of the sentence structures in which the words reside. (...) The program first determines the semantic weight of the concept from the dictionary. (...) After the semantic weight is determined, the program determines the concept's place in the text's syntactic structure to determine its overall relevance. Once a concept's relevance has been determined, the program follows more rules that compare the weight of all the concepts within a text, and generates summaries based on the relevance of all its concepts to produce the desired output."
This could be a machine-generated replacement of the meta description tag, that was mostly used to mislead search engines. It's the core essence of a page expressed using portions of the text.
The screenshot below shows a search result for [Twitter], a snippet generated by the search engine and an abstract produced by Syntatica.