Here's what I think it means in just a few words.
When Google started out they used an analogue of academic citation to analyse the internet. The more backlinks from other pages that any page had the better that page was likely to be.
Later Google started to try to use quality measures to try to improve the resolution of their results, so that a crappy page with a load of crappy links would not always rank higher than an authoritative page with few links from other authoritative sites.
Then (or maybe at the same time) Google understood that people are irrational creatures and that the most authoritative sites/pages were not always what people wanted. (after all there are people who believe in astrology, fairies and magic money making schemes so no shortage of irrational people wanting to scratch an itch)
So Google started mining social bookmarking and similar sites with a view to crowdsourcing their results.
Now Google is becoming explicit. They are moving toward a web where quality of results is not going to be measured on the authority of a page based upon expertise and fact but rather where enough aunt Sallys and cousin Berts mention how well a page suits their aura then that page will become well ranked.
LINKING is becoming less important than LIKING. The problem is that people who link to things from web pages usually have some expertise and a commitment to the field of knowledge (even if it is a page about birthstones). LIKING requires much less expertise and much less commitment and thus, IMHO the overall quality of results will tend to go down but more people will be happy with what they get. (and they will get rubbish)
If this sounds in any way elitist or patronising I apologise, but what we are seeing now is a dumbing down of the internet.
So now, we go out and get people to 'LIKE' our pages, get folks to Twitter about them and we game the system in different ways than the ones we used before. We are already seeing that with the use of 'reveal' tabs in Facebook where, unless we click a 'LIKE' button we do not get to see the content of the page.
How messed up is that, blackmailing visitors to LIKE something they have not yet even seen. 