A summery break is like a winter break but warmer. A summary break is, I'm pretty sure, what Elo meant by a page-separation line.

If your article looks like A [summary break] B, then:

• When it appears in a list of articles, A will appear along with a link to the full article.
• When it is viewed on its own, you will see A and then B.

It doesn't produce any visual separation beyond an ordinary paragraph break; if you want more than that, you could e.g. put a horizontal rule after the summary break and before B.