Essentialism is a philosophy held by Wikipedians who think that the arguments over notability are especially silly given that there's so much left to do on the big general articles for which a consensus exists that they are essential. Essentialists believe that Wikipedia is not paper, but an encyclopedia, and that does mean that not everything qualifies for inclusion, regardless of space limitations or lack thereof. Therefore, its role is to cover topics which are not only encyclopedic but also notable and verifiable, and if that means that Wikipedia isn't the first to cover a topic, that's actually probably a good thing - one shouldn't have to question the value of inclusion of the content.
They believe that the wiki concept was meant not only to be able to do everything that a paper encyclopedia does but also expand on it, but that being said, there are always going to be parameters. Essentialists believe the main reason for Wikipedia 1.0 is because it's become largely apparent that enough energy has been spent on breadth, perhaps at the expense of depth within the articles which are clearly the core topics. They think that the deletion/inclusion divide should be forgotten until there's less to do on the basics.