(for the newbies) These are meant to be added in the <head> section. And a little wiki: Many sites, in particular search engines, use spidering as a means of providing up-to-date data.
Canonical<link rel="canonical" href="http://luvnishthegreat.com" />
This tells the web spider that the page the canonical points to is the preferred version of that page, or the original version of that page, or a copy of that page. It is especially useful to avoid duplicate content on the site.
Publisher<link rel="publisher" href="https://plus.google.com/100546055913672743828" />
The long numbered link which makes no sense is the link to my Google plus profile. It tells Google's pet crawler that this Google+ account holder is the owner of that website. Hence, you get a pretty little thumbnail picture of yourself in the search results (awww.. cute!) Research has shown that having your picture next to it displays trustworthiness and heightens your chance of getting clicked on google search.
META description<meta name="description" content="description of the page" />
Pretty self-explanatory. The max length of the description is 156.
META language<meta name="language" content="#language">
Replace the #language with 'English', 'French', 'Spanish', 'Hindi', etc.. as would suit your site.
META Classification<meta name="classification" content="#field">
Replace the #field with what you deal in. E.g. 'business', 'blog', 'hotel', 'gaming', etc...
META Owner<meta name="owner" content="Luvnish the great">
This is not THAT necessary, but it is nice to have coupled with the G+ publisher identification.
OpenGraph Meta tagsBasically are tags which are useful for facebook (and bing as a result). I'm listing them below; they do not require much rantings:
<meta name="og:title" content="Le SEO" />
<meta name="og:type" content="blog" />
<meta name="og:image" content="link thumbnail picture I want next to my facebook shares" />
<meta name="og:description" content="Search engine optimisation through my eyes..." />
'Next' and 'Previous' tagsThese 2 are tags which are used on website pages which have a follow-up on the next page, i.e. a next and previous button at the bottom (like a blog).
For instance, on a page 3 of a blog, the following tags would be present in the head:
<link rel="next" href="http://whynotseo.blogspot.com/?page=4" />
<link rel="previous" href="http://whynotseo.blogspot.com/?page=2" />
This tells the search engine crawler where this page stands in the list. It is also useful to avoid duplicate content.
There are more to this. I shall attempt to populate this list for you, wonderful people who stumbled upon the right place, in due time. As proof, the list in the post below did lengthen, if you happened to read it before.