A publicly listed company is a business owned by shareholders who buy and sell shares through a stock exchange or over-the-counter market. A public company is the opposite of a private business owned by one or more individuals where shares aren't traded on the open market.
Companies become publicly listed through an initial public offering, or IPO, process. When shareholders begin trading openly, sentiment on the future prospects of the business impacts the perceived value of ownership. When positive sentiment prevails, shareholders tend to buy and drive up the share price. When negative sentiment or news take hold, the share price tends to fall under selling pressure.