What does Needs Met mean?
Search engines are there to help you and I find what we are looking for. To do so they need to constantly evaluate which pages meet the needs of which query best.
So if I search '20C in F' then it's pretty obvious that I am looking for a temperature conversion but a very specific one rather than a table of conversion values.
If I click on the third search result and find the answer my 'needs have been met'. Search engines can see this because I don't click the back button and then chose a different result to click on.
Now say 50% of people who carried out the above search clicked on the first link in the search results but then hit the back button while 20% clicked on the 3rd result and never hit the back button this sends the search engine a clear message - the third result meets the needs of this query better than the first result.
The search engine then knows, once it has gathered enough data to be sure, that what is now #3 in its search results should be #1 and it adjusts accordingly.
Now our new #1 might not have as much authority (in terms of quality links) as the website it has just deposed but the concept of 'needs met' overrides this.
Some search engines like Google have taken this a step further. The Google Knowledge Graph scrapes what it sees as the relevant piece of information out of a top ranking page and serves it up right there and then in the search results page.
It can test whether or not what it scraped is 'needs met' by watching to see if a user ignores the information and clicks on another link. If so it adjusts the knowledge graph information accordingly and waits to see if it is more or less successful.
Automated needs met learning by search engines is thought to be one of the next stages by which links (which to some extent can still be gamed) are given less importance.