Most securities have a real intrinsic value that can be calculated the future cash flows to owners from that security. For bonds, the number of variables in this calculation makes this easier to understand: If you have a bond that will pay you $100 one time in one year, then the intrinsic value of that bond is slightly less than $100 (because there is risk you won't be repaid, there is inflation, and there is a cost to waiting to get your $100). If you pay $50 for it, you are getting a very good deal relative to intrinsic value, and if you pay $150, you are getting a bad deal.

This same calculation can be made for stocks based on their dividends and any terminal value from an eventual acquisition. These calculations fluctuate more because dividends are variable.

The parent's comment is right though, its something buffet often observes: If a company buys back stock far about its intrinsic value, it is transferring wealth from current shareholders to now ex-shareholders. If it buys it back below intrinsic value, then it is transferring it from now ex-shareholders to shareholders.

There is actually a wonderful story that illustrates this. Try searching for "buffet pritzker Rockwood & Co arbitrage".

The short version is that Rockwood & Co was sitting on a massive supply of very valuable chocolate, and its stock price didn't reflect the value of that chocolate. Pritzker controlled the company, and announced it would redeem shares for chocolate (a buy-back in chocolate). Arbitrage traders then bought up shares at the low price, redeemed them for more valuable chocolate, and pocketed the difference.

BUT, what they didn't calculate was that the amount of chocolate that remained inside the company was far larger than the amount that was going out to the departing shareholders. Essentially, the chocolate 'payments' for stocks were far below the intrinsic value of the company. So, every time an arbitrage trader traded in shares for chocolate (at a profit to them) Pritzker was actually getting far richer by retaining his remaining shares. Everyone was winning, but Pritzker was winning far more. In the end, Pritzker retained a much higher ownership percentage of an only slightly smaller stockpile of very valuable chocolate, and made a lot doing it.

I think I saw the full version of this story in the biography of Buffet, but I am not sure. It is super fun. It illustrates why a management team that is buying back shares below intrinsic value is helping the remaining owners increase their wealth, and vice versa.