What is Initial Public Offering?

Legal Definition
Initial public offering (IPO) or stock market launch is a type of public offering in which shares of a company usually are sold to institutional investors that in turn, sell to the general public, on a securities exchange, for the first time. Through this process, a privately held company transforms into a public company. Initial public offerings are mostly used by companies to raise the expansion of capital, possibly to monetize the investments of early private investors, and to become publicly traded enterprises. A company selling shares is never required to repay the capital to its public investors. After the IPO, when shares trade freely in the open market, money passes between public investors. Although IPO offers many advantages, there are also significant disadvantages, chief among these are the costs associated with the process and the requirement to disclose certain information that could prove helpful to competitors. The IPO process is colloquially known as going public.

Details of the proposed offering are disclosed to potential purchasers in the form of a lengthy document known as a prospectus. Most companies undertake an IPO with the assistance of an investment banking firm acting in the capacity of an underwriter. Underwriters provide several services, including help with correctly assessing the value of shares (share price) and establishing a public market for shares (initial sale). Alternative methods such as the dutch auction have also been explored. In terms of size and public participation, the most notable example of this method is the Google IPO. China has recently emerged as a major IPO market, with several of the largest IPOs taking place in that country.
-- Wikipedia
Legal Definition
The first public offering of a companies stock in the market. A retail client will buy the stock and sell it to their customers. Refer to addon and rights issues.