An ultra-libertarian is most likely a person who may agree with 100% of all the libertarian views and does not believe in anything else. Also, they may have other idealogies along side that such as anacho-capitalism; this means very little or no government intervention with in economics and market capitlaism what so ever. Overall, it is a libertarian minded person that truly believes in it and nothing more.
This answer is my personal guess, but I hoped that this has helped.