If your website were a person, who would it be? Is it serious, buttoned up, all business, yet trustworthy, and capable? Is it a wisecracking buddy that makes evan mundane tasks fun?
Following a similar structure as a user persona, you can flesh out the personality of your design by creating a design persona. Personality can manifest itself in an interface through visual design, copy, and interactions.
A design persona describes the methods of channeling personality in each of these areas, and will help a team of web professionals construct a unified and consistent result.