What is the "General Magisterium" in Roman Catholicism? I understand that there are three magisterium in Roman Catholicism.

What is the General Magisterium according to Roman Catholic belief?
I hadn't heard of (or recalled) three layers of Magisterium until seeing this question (and I was hoping someone who was more familiar would post and answer sooner), but I was able to find a page (just one) that refers to three levels. Effectively, this resource claims that the General Magisterium, i.e., the general teaching authority of the Church on faith, is the full body of Baptized and confirmed and/or ordained Catholics.

http://www.catholicplanet.com/TSM/general-magisterium.htm


  The general Magisterium
  
  a. seeks the truth fallibly, includes the possibility of significant
  error, but is guided by the Holy Spirit. b. this search for truth has
  the charism of certain fruitfulness. The faithful who seek new
  insights into the Faith, in accord with the teachings of the
  Magisterium proper, cannot fail to bear fruit that will last. c. is
  exercised by all the faithful by virtue of the Sacraments of baptism,
  confirmation, or ordination. d. is expressed in speculative theology,
  in discussions among the faithful, in sermons by ordained persons, and
  in non-official writings and discussions of Popes and Bishops. e. The
  Holy Spirit guarantees that this search for new insights into the
  truths found within Tradition, Scripture, and the teachings of the
  Magisterium proper will bear fruit that will last. f. assent is not
  required, except that all the faithful are required to assent to a
  sincere search for truth within Tradition, Scripture, and the
  teachings of the Magisterium proper g. anyone may dissent from
  particular ideas expressed in speculative theology, but no one may
  entirely dissent from the sincere search for truth within the Faith


However, as the author begins to summarize this in more plain English, he uses a concept we more commonly hear of, and which can be found more directly in the Catechism and other documents.


  The difference between the proper Magisterium (the Sacred Magisterium
  and the Ordinary Magisterium) and the general Magisterium is analogous
  to the difference between the priesthood of all ordained persons and
  the priesthood of all the faithful.


The Church teaches that we're all (Catholics) called to be priests, prophets, and kings to some extent. As laity, we're much more limited in our authority and jurisdiction, of course. But, we do have a call to participate in these roles, and therefore a call to teach faith -- more accurately, to forward and/or extrapolate in a non-authoritative manner on the faith, which is taught authoritatively by the higher level(s) of the Magisterium.

The Catechism of the Catholic Church talks more about the hierarchy and the three roles of all Catholics, but doesn't phrase it in terms of levels of the Magisterium so directly. See Christ’s Faithful—Hierarchy, Laity, Consecrated Life if you're interested in that.