Term for “preview entries” that web sites show on index pages?

Blogs and websites typically provide an index page of entries where they show an excerpt of the post. Excerpts usually include title, author, post date, and a blurb. What is the term for these sorts of excerpt?

I’d call them snippet views. The Macmillan dictionary gives this definition for snippet:

snippet — a small piece of something, especially information or news

A more formal name used for these types of items in the non digital realm is "abstract". It's not wrong in the digital world, but I don't remember seeing it used. I do remember seeing "summary" or "capsule".

Browsing through WP's entries on RSS and its ontology, what we first find is that the collective term for the kind of information these entries present is (unsurprisingly) "metadata", and that while RSS metadata is well-defined, there is no universally accepted term for a standardized set of specific metadata elements which could be used in a blog index to summarize a post (nor consensus on which elements should be included in such a standard set). So, from these abstract sources, the best we can identify is:

post description

or

post summary

If we can't find a normative definition, perhaps we can get a clue from how these concepts are applied (and named) in practice, by inspecting the source for a few open-source feed readers.

Doing so reveals they, too, use generic terms like "news item", "preview", "description"¹, or "abstract" (as @brasshat indicates), and in general do not have a concept of "standardized set of metadata used to summarize a post" separate from "the post itself"; it seems typical to have a blog post object carry around its own metadata side-by-side with its content (or a link to its content), and selecting which metadata to summarize or describe the post is treated as a presentation-layer issue (often user-configurable; the only field definitely not included in a summary is the content of the post itself). So it seems these codebases are a dead end², and the only novel word to arise from investigating them is:

post preview

Taking another tack, then, we can try tracing the ontology of blog software to its roots: journalism. In paper journalism, we again have the concept of "metadata": "headline", "dateline", "byline", and so on.

Since this metadata is fairly fixed and limited relative to the more abstract concept in software, perhaps we can find a single word to describe the totality of a given article's metadata, which would serve our purpose, so long as it enjoys some respect or at least currency in journalism.

Unfortunately, it seems we're stymied here again, for similar reasons: each individual piece of metadata has a well-defined name, but there doesn't appear to be a single word that describes the metadata in toto. With that said, there are some novel and interesting contenders; one glossary of journalism and media terms has:

bulletin: a short official statement or broadcast summary of news.

Which, sadly, appears to communicate the entire news item, as opposed to just introducing it. Moving on, we encounter:

tease: Material promoting a story which ‘teases’ the reader or listener by hinting at but not revealing the full story.

or

teaser: A short segment produced to advertise an upcoming news bulletin or news items.

Which, while it could be pressed into service, because it's intended promote the piece by not revealing the whole story, i.e. "tease" the reader into clicking through, in practice this would be applied more to an Upworthy-style headline (in the digital age) than an abstract of the post.

So, we come to the final, perhaps most interesting item (for its obscurity if nothing else):

nut graf: A paragraph telling the essential elements of a story briefly, i.e. ‘in a nutshell’.

Cute? Yes. Necessarily communicating all the relevant metadata ... probably not (this would more likely correspond to the "description" meta-element of RFC 5013, rather than the whole set of elements).

¹ Though unfortunately these terms are also used as the metadata labels themselves, as they apply to the blog as a whole, as in url="http://www.fool.com", description="To Educate, Amuse, and Enrich".

² Now, this may be an artifact of my decision to inspect feed readers, because readers typically defer the hosting of content to the blog (fetching it as needed), and their concept of "news item" is identical to "a user-friendly summary of a news item" (as reflected in the schemas of the projects linked to, above). So if you're still in need of an appropriate word, you might have better luck digging through the codebases of blog software proper.

In the context of the index, like on the same page, individual entries could be referred to as posts, in the sense that they represent the actual post.

It depends on the layout and other aspects of the site whether it’s particularly obvious that they only represent the actual posts and cannot be mistaken for something else.