Something that's blank is empty or undecorated. A blank canvas hasn't been drawn or painted on yet — it's clean and unmarked.
A blank computer screen has no information on it, and a blank look on someone's face is completely free of any expression, revealing nothing. If your mind goes blank during a job interview, you are left without any thoughts for a moment. When blank is a noun, it means "a line to be filled in" or "an empty space." In the 1500s, a blank was the empty, white center of a target, from the French word blanc, or "white."