Originally, a company issues equity (shares) of itself in exchange for cash. Equity is ownership of the company, whoever owns the equity (shares/stock/whatever form it is) owns a piece of the company. A buy back is what it sounds like, the company gives investors cash to buy back the equity it initially issued, thereby concentrating ownership back in the original owners. This is frowned upon mostly (I would argue) because it does not provide any economic benefit except to the shareholders who receive the cash, and the original owners who now have my ownership. Everyone else loses, that cash could have gone to making the company more efficient for society, gone back to employees, etc. Put another way, a buy back benefits those who typically already have more wealth than those without (shareholders and owners of a company are probably more wealthy than most others of course).

So basically buy backs "only benefit the rich," which is why they are frowned upon. How true is this claim? Research more and decide for yourself.