Stocks were portions of a company that could be bought and sold.
In 2269, Spock cautioned against returning Captain John Christopher to 1968 Earth with his newfound knowledge of Human history, as a man with such knowledge could manipulate stocks, industries and nations. (TOS: "Tomorrow is Yesterday")
In 2364, Ralph Offenhouse recalled that several cryonics companies suffered when their refrigeration systems failed as a result of power failures. This cause their stocks to fall. Though he believed his stock in the company he chose to preserve him had split at least a dozen times since he was frozen, Data assured him that the entire industry did not last beyond the mid 21st century. (TNG: "The Neutral Zone")