ss is for spiteful sprit, and mm is for minion master
ss is most often seen in use with mesmer as second class to use echo to essentially spam SS on as many enemies as possible while they literally hack away at your tank and in turn kill themselves.
mm is just what is sounds like a necro who raises as many minions as possible, if you have a monk with heal area, or another necro to recharge your energy with bip or ritual, you can raise a rediculous army of undead, they do however have a terminal health degen.