Wealth measures the value of all the assets of worth owned by a person, community, company or country. Wealth is determined by taking the total market value of all physical and intangible assets owned, then subtracting all debts. "What is Wealth", Investopedia
Wealth does not measure the inherent value of an asset, only its market value at a particular point in time. Sources of wealth include real estate, stocks, bonds, bank deposits, pensions, and mutual funds. One's own home is the main source of wealth for the majority of Americans, except the most affluent. Check it out:
Source:Wealth inequality and monetary policy by Dietrich Domanski, Michela Scatigna and Anna Zabai Bank for International Settlements 6 March 2016. Accessed at https://www.bis.org/publ/qtrpdf/r_qt1603f.htm
According to a recent report by the Bank for International Settlements, housing and stockholder equity have been the most important drivers of inequality over the last few decades. In other words, inequality mostly tracks the ups and downs of the housing and stock markets - meaning inequality goes up during market booms and goes down during busts.
Since the very rich make so much money from their investments (mostly real estate and stocks), their income goes way down during market busts. That's a problem for countries with highly progressive tax systems: tax revenue plummets just when additional safety net revenue is needed. A double whammy.