"we have added a new Modern Quilting category to the competition."
-- Why? What prompted the committee to add this new category? If you can answer those questions, it could give you direction to come up with the description/definition.
But it may not be possible to prevent a quilt from fitting more than one category. If that's the case then perhaps a requirement for the quilter to pick the best category for the quilt -- but the committee reserves the right to move the quilt to a more appropriate category if the committee feels it was entered into the wrong category. But that will really open up the committee to hurt feelings and cries of favoritism.
Not knowing what the rest of the categories and descriptions are, I'm with Holice on this one.