What Does "Per Stirpes" Mean?

Does your Will or trust contain the phrase "per stirpes"? Did your attorney explain what it means? Have you forgotten by now? Stan Rule, an estate planning and elder law attorney in Canada, has a great post explaining clearly what this phrase means and some of the ways it can be misused. 
He writes, in part:

I sometimes use "per stirpes" to describe a method of distributionamong issue (in other words children, grandchildren, greatgrandchildren etc.) For example, I might direct my trustee to give whatis left of my estate after paying my debts and funeral expenses to“those of my issue who survive me per stirpes.” When I write this, Imean that my estate will be divided equally among my children, but if achild has died before me, that child’s share will be divided equallyamong those of his or her children (my grandchildren) who are alive atmy death. If both a child and one of that child’s children die beforeme (“my deceased grandchild”), then those of my great grandchildren whoare the children of my deceased grandchild will share the portion thatwould have gone to their parent.

As you can see, using "per stirpes" is a lot simpler than trying to include in a Will or trust all of the different possibilities that could arise, but it needs to be used correctly or it could lead to problems down the road, as Stan points out in his article.