There's a very consistent definition for what that means with plenty of papers and institutions that use use roughly the same definition. Here's one phrasing of it by the OECD[1]. Basically it's just income minus taxes, what part of that is remotely vague?

Discretionary income might be an even better measure but that has more wiggle room on defining what is a necessity and not.

https://data.oecd.org/hha/household-disposable-income.htm [1]

I still don't see how that's a good metric, in any way, for judging health care costs. "Disposable income" takes nothing else into account such as other costs or predatory behaviors in the healthcare system

Its literally just money after taxes, and most people are living paycheck to paycheck

You can't judge how much of a burden healthcare costs are unless you account for how much of a person's income or some proxy of it healthcare is. Just saying that the US spends more per capita than other OECD countries doesn't say anything without more context. IF you want to show that the healthcare spending isn't efficient in the US you have to at least show that it's not just because everything costs more there or that everyone earns more in the US (gdp/capita is higher than ~85% of OECD in US).

It spends more per capita with worse outcomes

That's the point, where is that extra spending going? What good is it doing? Why is any other question the topic of discussion?

You haven't shown its extra spending with just that one stat. Does $50 USD buy you the same things in the US as $50 USD in Venezuela?

That's exactly what I'm talking about, it doesn't. Why not?

Does Venezuela have a bunch of leeching middlemen at every possible point in their systems due to the massive push for privatization?