When someone tweets a link from your website, Twitter can use Twitter Cards to attach rich photos, videos and media to Tweets.

By doing some minimal configuration changes on your Drupal site using the Metatag Module and the Twitter Cards submodule, users can see a “Card” added below the tweet that contains neatly formatted information coming from your website, as shown in Image 1 below.

The cards are generated using HTML markup in the HEAD region of your Drupal site; that’s why the Metatag module is used.

Twitter will scrape your site and generate the card using the HTML meta tags.