Two of the 100 tiles in English-language Scrabble are “blanks.”

 

You may use them as any letter you wish. This makes them extremely valuable. When playing a blank, you will be shown a pop-up menu to designate which letter you would like the blank to become. The blank remains that same letter for the rest of the game. Blanks are worth zero points regardless of which letter you choose, but their flexibility more than makes up for it.