Definition 1
The procedure by which an Underwriter brings a new security issue to the investing Public in an Offering. In such a case, the Underwriter will Guarantee a certain price for a certain number of securities to the Party that is issuing the security (in Exchange for a fee). Thus, the Issuer is secure that they will raise a certain minimum from the issue, while the Underwriter bears the Risk of the issue.
Definition 2
The process of insuring someone or something.
Definition 3
The process by which a Lender decides whether a potential Creditor is creditworthy and should receive a Loan.