Embedded Tweet feature allows websites to generate copy and paste-able HTML markup to render a Tweet on any third-party website.
https://dev.twitter.com/docs/embedded-tweets
Widgets
Get access to data on 232,203 websites that are Twitter Embedded Tweets Customers. We know of 35,697 live websites using Twitter Embedded Tweets and an additional 196,506 sites that used Twitter Embedded Tweets historically and 24,040 websites in the United States.
Get a list of 232,203 websites using Twitter Embedded Tweets which includes location information, hosting data, contact details, 35,697 currently live websites and an additional 610,630 domains that redirect to sites in this list. 196,506 sites that used this technology previously and 24,040 websites in the United States currently using Twitter Embedded Tweets.