Pillars of Wealth are the various repositories of value in which you store and build wealth over time. You can simply think of them as assets. The concept of Pillars is a metaphor. Think of stout pillars or columns supporting your family's financial well-being.
Pillars include retirement accounts, cash, real estate, college savings plans, etc.
Your objective should be to accumulate as many Pillars (or assets) as you can over your lifetime.