Publius means "public" in Latin, and is a nod to both the open nature of Wikipedia and to the pseudonymous authors of the Federalist Papers. Digitus means "hand" in Latin, and also refers to the digital nature of Wikipedia. This makes the whole name something like "public hand". But then again I don't actually know Latin. Mostly I was just struggling to come up with a username that wasn't already taken. Anyway...
Be excellent to each other!