The Biden administration has issued an ultimatum to TikTok, a popular social media app with over 100 million US users, to be sold by its Chinese owners or face a ban across the US. The move is in response to security concerns posed by the app's Chinese ownership, and marks a possible turning point in the long-running negotiations between federal officials and the company. TikTok has expressed disappointment with the ultimatum, and it remains to be seen how the company will respond.