This appears to be the study that the figures are taken from: http://www.levyinstitute.org/pubs/wp_589.pdf

And here's the definition of wealth:

I also use a more restricted concept of wealth, which I call “non-home wealth.” This is defined as net worth minus net equity in owner-occupied housing (the primary residence only). Non-home wealth is a more liquid concept than marketable wealth, since one’s home is difficult to convert into cash in the short term. Moreover, primary homes also serve a consumption purpose besides acting as a store of value. Non-home wealth thus reflects the resources that may be immediately available for consumption expenditure or various forms of investments.