"Embedded on these websites" is the new feature being tested by Twitter to show links to the articles that have embedded the tweet. Since, Twitter is becoming a news source for many; a feature that curates the content behind the topic is going to be beneficial. Twitter has made no formal announcement of the feature.
Are you Using Embedded Tweets?
Embeddable tweets will offer some publishers a new way of gaining exposure on a topic. Embedded tweets let users to insert an interactive tweet within the article that has media like video, photo, and show real-time retweets & favorites. It also makes it easier for the user to engage with the tweet within the article.
To embed a tweet, you just have to click on "more" link and choose "embed".Twitter Testing "Embedded on the websites" Feature!,