PFMG is a parallel semicoarsening multigrid solver similar to SMG. See [&make_named_href('', "node39.html#SFAshby_RDFalgout_1996","[1]"), &make_named_href('', "node39.html#RDFalgout_JEJones_2000","[5]")] for details on the algorithm and its parallel implementation/performance.
The main difference between the two methods is in the smoother: PFMG uses simple pointwise smoothing. As a result, PFMG is not as robust as SMG, but is much more efficient per V-cycle.