I'll take a stab at it. One of the people near the front of the chamber who actually know all of "the rules" (the unchanging ones) and protocol that Congress is supposed to follow. Considering there are members of the House who don't even know basic American civics, I'm sure there are many who don't know "the rules."
I think you are referring to the Parliamentarian, but I don’t think that is who the original post is referring to.