Post Summaries versus Excerpts
A post summary is a small bit of representative text for a post. It could be a description about what you wrote. A post excerpt is a literaly an extract of the post.
I make a distinction between the two. A summary is for sharing, for telling other people what you did. It's often of the form "I wrote a post on X, please read it". The excerpt is really an internal concept, an extract of your post. How it's used varies, but I use it for displaying posts in a list on my blog.
A "summary" is a marked up bit of text for the IndieWeb. It's a meta tag for the Open Graph (OG) Protocol, called the "description". Like OG image versus the featured image, if you are coming from the IndieWeb you have the problem of having to embed data into your posts that is only used as metadata, so you may have to hide it.
In the past I called the "summary" the "blurb" in my blog. I may change that.
I also conflated "excerpt" and "summary" but I think I need to fix that.
It is possible to use the "summary" or "description" as your representative text in your posts lists on your blog. I've been using the excerpt for that, but I don't have to. It would make my posts lists look like my Twitter or Facebook wall, which is a look, and some people may like that, but it's not what I'm going for.