Off the cuff reply: I'd say that anybody with a six figure income is well off; anyone in the quarter mil area is wealthy, and anyone with an income of a million dollars a year is rich going on super rich. Wealth is accumulated in two ways. Much wealth is created by hard work, but a lot of wealth is not created; it is merely transferred.
You answered the second half of the question; however, I will ignore the lack of response to the question of, "What is 'wealth'?"
Now, before we get to transfers, lets work through the following logical deduction:
It appears safe to say the following.
If A accumulates wealth in a just manner and transfers it to B in a just transfer, then B justly accumulates B's wealth.
Now, if B transfers his wealth to C in a just transfer, then C justly accumulates C's wealth.
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n justly accumulates n's wealth.
This is correct, is it not?
Now, let's define wealth as a nominal commodity that represents both property and the power to purchase property. Thus, one could own 100 head of cattle; they are both property and purchasing power.
Well, one characteristic of property is the ability to do with one's property what one desires: this is entailed in ownership, is it not?
If one can do with one's property what they so desire, then one can transfer their property however they desire. Thus one can bequeath their property; and, such a transfer is just.
Now, for other transfers. What constitutes an unjust transfer?
B steals A's car and sells it to C. C has a fake title made for the car and sells it to D. D sells the car to a used-car dealership, where E eventually buys it. Has E committed an injustice? No. Is the transfer unjust? This appears tricky; an injustice has certainly been done to A. B, C, and D appear to knowingly and willingly be dealing in stolen merchandise. However, the dealership and E have done nothing wrong. In fact, the transfer between the dealership and E appears to have all the characteristics of a just transfer. In fact, to take the car from E to give it to A, without reimbursing E, would be unjust. To make the dealership reimburse E, would be unjust to the dealership. The only remedial course that could be taken would be to identify each link in the chain of transfers, passing the car back to A and reimbursement up from at least D.
This is analogous to the claim that many make of wealth in America: it was accumulated over centuries through unjust and oppressive means and, therefore, it must be redistributed to level the playing field. Yet, there are many (I would claim the vast majority) with wealth in America who have themselves done nothing unjust in accumulating their wealth. Seeing as the only remedial course from the example was to take from those who actually committed injustices, while reimbursing those who unknowingly benefited down the line, then we would have to identify those sources of injustice. I am going to posit that most of those sources are long dead; therefore, they cannot reimburse anybody. Thus, there is no just remedial course. There is simply the option to understand that **** happens and be vigilant with regard to current injustices, or there is the option to compound past injustices with current injustices.