A company or other entity that administers the public 
issuance and distribution of securities from a corporation 
or other issuing body. An underwriter works closely with 
the issuing body to determine the offering price of the 
securities, buys them from the issuer and sells them to 
investors via the underwriter's distribution network.
                        (Or)

Underwriters generally receive underwriting fees from their 
issuing clients, but they also usually earn profits when 
selling the underwritten shares to investors. However, 
underwriters assume the responsibility of distributing a 
securities issue to the public. If they can't sell all of 
the securities at the specified offering price, they may be 
forced to sell the securities for less than they paid for 
them, or retain the securities themselves.

underwriters are mad guys

A financial institution which, in return for a fee or 
commission, agrees to purchase unsold shares in a new 
issue, if the issue is not fully subscribed.

Underwriter is someone who takes financial risk in return 
for fee on behalf of the issuer. And their work is rasising 
capital from the investors/public to the corporates or 
government institutions.

Underwriters are mainly financial institutions which 
promises to purchase a particular company's shares if they 
are not sold in particular time.