In its blog post, Twitter says that the content showing on the Discover tab is being sourced, in part, by algorithms identifying tweets that are popular among the user you follow, and the users they follow.
Next to each popular story, you’ll see context on why it’s there, such as the Twitter avatars of your contacts that have shared the story. There are also links to view popular tweets about the story or to tweet your own response to it.
In a separate post, Twitter’s engineering folks explain in a bit more detail how the new Discover tab works. The first step, they say, is
…to identify your connections and rank them according to how strong and important those connections are to you.
Once we have that network, we use Twitter’s flexible search engine to find URLs that have been shared by that circle of people. Those links are converted into stories that we’ll display, alongside other stories, in the Discover tab. Before displaying them, a final ranking pass re-ranks stories according to how many people have tweeted about them and how important those people are in relation to you. All of this happens in near-real time, which means breaking and relevant stories appear in the new Discover tab almost as soon as people start talking about them.
On many occasions in the past, Twitter has discussed its desire to improve content discovery on the site — especially when the company has rolled out new versions of its home page and/or other updates to the Twitter.com user experience.
This latest update involving more personalization appears to be coming from the Julpan team that Twitter purchased last year.
Twitter says these changes on the Discover tab will be rolling out on Twitter.com and its iPhone and Android apps in the next few weeks.