In corporate finance, a listing refers to the company's shares being on the list (or board) of stock that are officially traded on a stock exchange. Normally the issuing company is the one that applies for a listing but in some countries the exchange can list a company, for instance because its stock is already being actively traded via informal channels. Initial listing requirements usually include a history of a few years of financial statements (not required for "alternative" markets targeting young firms); a sufficient size of the amount being placed among the general public (the free float), both in absolute terms and as a percentage of the total outstanding stock; an approved prospectus, usually including opinions from independent assessors, and so on. Stocks whose market value and/or turnover fall below critical levels can get officially delisted; delisting is often the result of a merger or takeover, or the firm going private.
Delisting refers to the practice of moving in the stock of a company from a stock exchange so that investors can no longer trade shares of the stock on that exchange. This typically occurs when a company goes out of business, declares bankruptcy, no longer satisfies the listing rules of stock exchange, or has become a private company after a merger or acquisition, or wants to reduce regulatory reporting complexities and overhead, or if the stock volumes on the exchange from which it wishes to delist are not significant. Delisting does not necessarily mean a change in company's core strategy. In the United States, securities which have been delisted from a major exchange for reasons other than going private or liquidating may be traded on over-the-counter markets like the OTC Bulletin Board or the Pink Sheets.