The process that a company goes through when moving from private to public. This is known as "going public". It is when shares are first sold to the general public.
Companies that operated privately often decide to raise money through an IPO. It is often done to pay of debts, fuel expansion, or to cash the original founders or investors out. Venture Capital firms regularly invest in start ups with the intention of them going public. This is often how they generate their return for the capital invested.
After the IPO, the ownership of the company is now public.
It starts with a company, once it makes the decision to go public, to find a lead underwriter. This is the one responsible for assembling the syndicate, the banks responsible for selling the offering to institutional and individual investors.