Realistically, it means a new way to play, especially since the text on the button is deliberately blank and it wouldn’t be something as simple as “Options” or “Exit.” But what will it be? We have no idea. But you can join in on the speculation yourself.
Hearthstone, the little title screen offers you three options. That hasn’t changed and no one has really expected otherwise; you can play the main game, enter the arena, or take on a solo adventure. Of course, when the official Twitter account for the game posts an animated GIF of a fourth menu option popping into place, you start to wonder what that option will mean.