Technologies behind Google ranking
Discusses some of the technologies Google uses to better understand the page, search query and users.
I think the most interesting area, as an seo, is the explanation provided regarding identifying critical concepts.
someone who searches for [rainforest instructional activities for vocabulary] is really looking for rain forest lesson plans.
Reality = what someone searches for is not necessarily the same query that google performs. Rank for a concept keyword phrase, and you get exposure for other queries that are not exactly the same. So in this case, optimizing for the long tail "rainforest instructional activities for vocabulary" would not provide visitors from google because they are actually searching "rain forest lesson plans". Because of this, some phrases may be impossible to rank for if the actual google search is a concept query. imo.