Marvel Entertainment is having an announcement of some kind scheduled for Thursday, January 26 at 10 a.m., as noted on their Twitter page.
Tomorrow. pic.twitter.com/uQnFjapziv— Marvel Entertainment (@Marvel) January 25, 2017
The teaser doesn't specify which of the many divisions of Marvel Entertainment this is for, so it could be anything from a publishing project, a television series, an animated project, a movie, a video game, or merchandise. However, given that the recently-created Marvel Studios Twitter account isn't also carrying this message, it could rule out something related to the theatrical Marvel Cinematic Universe.
Newsarama will report on the news as soon as it breaks.