Underwriting

Underwriting refers to the process that a large financial service provider (bank, insurer, investment house) uses to assess the eligibility of a customer to receive their products (equity capital, insurance, mortgage or credit). The name derives from the Lloyd's of London insurance market. Financial bankers, who would accept some of the risk on a given venture (historically a sea voyage with associated risks of shipwreck) in exchange for a premium, would literally write their names under the risk information which was written on a Lloyd's slip created for this purpose.
Once the underwriting agreement is struck, the underwriter bears the risk of being able to sell the underlying securities and the cost of holding them on its books until such time in the future that they may be favorably sold.
If the instrument is desirable, the underwriter and the securities issuer may choose to enter into an exclusivity agreement. In exchange for a higher price paid upfront to the issuer, or other favorable terms, the issuer may agree to make the underwriter the exclusive agent for the initial sale of the securities instrument. That is, even though third-party buyers might approach the issuer directly to buy, the issuer agrees to sell exclusively through the underwriter.
In summary, the securities issuer gets cash up front, access to the contacts and sales channels of the underwriter, and is insulated from the market risk of being unable to sell the securities at a good price. The underwriter gets a nice profit from the markup, plus possibly an exclusive sales agreement.