In this Sentance what does Fc stand for?

the Fc region is the region of an antibody that dtermines the function of the Ab.That is the initial antibody IgM is an excellent complement fixer, but is not as good foropsonization ( coating a bacterium ) as IgG.So the isotype switch means simply that although the IgM or the IgG would recognize the same antigen ( and that is in the hypervariable region called the Fab) the function of that antibody is dictated by the base of the Y shaped antibody in the region called the Fc region.. The cl of the antibody , e.g., IgM, IgG, IgA, IgE, and IgD is dictated by the Fc region ..the specificity is dictated by the Fab region////two antibody cles may have the same specificity for an antigen but different functions, complement fixation, opsonization, allergic reaction , etc