Short answers, pulled from the story.
An initial public offering is the process by which a privately held company sells shares to institutional and retail investors for the first time, transforming it into a publicly traded company. The company typically hires one or more investment banks as underwriters, who arrange for the shares to be listed on a stock exchange and sold to the public. After the IPO, shares trade freely on the open market.
Saudi Aramco's 2019 IPO is the largest in history by nominal proceeds, raising $29.4 billion. Alibaba Group's 2014 IPO ranks second at $25 billion, followed by SoftBank Group's 2018 offering at $23.5 billion.
The first IPO in the United States was the public offering of Bank of North America, which took place around 1783. Before 1860, most early U.S. corporations sold shares directly to the public without investment bank intermediaries.
An IPO pop is a rapid rise in share price on the first day of public trading, caused when a stock is offered at a price below what the market will pay. The theglobe.com IPO on the 13th of November 1998 is an extreme example: priced at $9 per share, it surged 1,000% to a high of $97 on its opening day. Underpricing generates investor interest but costs the issuing company potential capital.
A Dutch auction IPO allocates shares based on price aggressiveness, with all winning bidders paying the same price. Google used this method for its 2004 IPO. Other U.S. companies that went public via Dutch auction include Morningstar, Interactive Brokers Group, Overstock.com, Ravenswood Winery, Clean Energy Fuels, and Boston Beer Company.
American securities law establishes two quiet periods during an IPO. The first runs from the filing of the S-1 registration statement until the SEC declares it effective, during which insiders and underwriters cannot publicly discuss the offering. The second lasts 10 calendar days after the first day of trading, restricting earnings forecasts and research reports from insiders and underwriters.
The earliest known form of public share issuance is linked to the publicani of the Roman Republic, organizations whose ownership was divided into parts that were sold to investors and traded near the Temple of Castor and Pollux in the Forum. Their shares fluctuated in value and attracted speculators. The publicani declined with the fall of the Republic.