Publicly-traded companies are ones that have portions of ownership traded on public securities exchanges such as the New York Stock Exchange or the NASDAQ. Any investor with sufficient available funds has the ability to purchase shares of a publicly-traded company. On the other hand, ownership in privately-held companies can only change hands with negotiations between the buyer and seller.
The benefit of a company going public through an Initial Public Offering (IPO) is the greater availability to capital for the company and the greater degree of liquidity for investors. Publicly-traded companies are also more transparent as compared to privately-held companies.
While there are advantages, publicly-traded companies have much higher compliance levels and must regularly publish publicly-available financial and company-specific reports and must be regularly audited. Privately-held companies do not have such stringent compliance and reporting requirements.