The product is whiteboard sheets. They come on a roll, you rip one off and stick it to almost any wall surface, and it clings. You then write on it like a whiteboard, then the ink will dry permanently after a few minutes.
I and my peers use them in requirements discovery sessions. The walls fill up over time, so you can look at anything you have produced. The fact that the ink dries allows you to take them away and use them later for writing up results, and to keep as a record.
These are not a common item. Each new client we work with invariably says they have never seen them before. Our organization gets them from a supplier in Germany, the product packaging says Leitz.
Office Depot shows up as a source when you do a web search, and Amazon too, but actually finding them on their sites is difficult. Right now Amazon says they don't have any and don't know when they will.
If you look for them, don't confuse them with "instant whiteboards"; these are thick sheets that cling to a wall, but are erasable at any time, like a hard whiteboard.
But finding them is worth the effort, and I hope more people using them will make them easier to find.