Eleven

"That one there," Robin said. "It's a plus sign. So it's, like, addition or adding a new number or whatever." She's a little surprised Hopper hadn't already programmed his in but Robin suspects that he may not actually enjoy technology as much as she and Steve do.

"Pretty much whenever you see that in any of the apps. Um. Apps are...applications. It means whatever opens up when you press the button. But, yeah, whenever you see that symbol, it means adding something new."