By TheStreet Staff What Is a Stock Buyback? When a publicly traded company repurchases outstanding shares of its own stock on the open market (or directly from existing shareholders), this is known as a stock buyback. When a stock buyback occurs, two things happen immediately—the number of shares outstanding decreases, and the proportion of the company each share represents increases. In other words, after a buyback occurs, existing shareholders (assuming they didn’t sell any of their own shares back to the company) suddenly have an increased stake in the business, both in terms of their perce…