...but most people seem to blend them into one.
The first issue is that the superrich are quickly getting super richer. I believe that this is because they have rigged the game to increase the returns to those in control of the financial sector. This is increasingly leading to our being led by a plutocracy. This problem can be addressed politically.
The second issue is that there is a growing gap (gulf) between low earners and high earners. Middle income jobs are disappearing while low and high income jobs are growing. This problem is much harder to address. It isn't because of a policy. It is because technology is making some workers much more valuable and other workers much less valuable. The net result is that society is being split between people that can't ever hope to make $40,000/year and people starting their careers well above that.
I see examples of the latter in my personal life. My sister's three kids are in their early to mid-20s. The oldest has been in and out of college with no direction and no major. He's worked a series of retail and fast food jobs and has no prospects to earn a middle class income. Her second child finished college with a literature degree. She's working as an admin assistant and, barring marrying well, will also struggle to be in the middle class. The third child graduated with an engineering degree and started his career making in the low six figures. They will all live significantly different lives economically from how they were raised.