Excerpt from this article:
What’s a Screenshort? Essentially, it’s a chunk of text, screen-shotted, and embedded in a tweet. It’s become an extremely popular way to share a passage from a story. You could call it a Tweetcap, maybe. But I’m going with Screenshort.
Embedding a text block means that people will read the thing you want them to read without having to follow a link. It, genuinely, saves a click (without being condescending!).
It’s also an effective way to highlight a passage. There have been all kinds of attempts by different websites to make individual passages and paragraphs linkable, but nothing has caught on. A Screenshort goes right where you want it to.