See Chapter 4: Wickeds, for more information.
In short, Wicked Paralogos are Paralogos of any word categorization level who were consumed by their own -mostly negative- wordfocus.
In general, Wicked Paralogos are Paralogos whose magic would be able to directly ruin somebody's life and/or cause mass destruction.
Being a Wicked Paralogos means that the Paralogos has been consumed by their word focus. This will happen with all negative words at this power level.
However, with neutral/positive words this wouldn't be a necessary process and would rather show a negative external influence, a failing of character from the Paralogos themselves or similar.