What is an Insurance Broker?

InvestorWords
Insurance Broker:  an independent agent who represents the buyer, rather than the insurance company, and tries to find the buyer the best policy by comparison shopping.

The New York Times Dictionary of Money and Investing (by Gretchen Morgenson and Campbell R. Harvey)
Insurance Broker: a broker, independent of any insurance company, who represents the interests of the buyer in searching for insurance coverage at the lowest cost and providing the highest benefit to the buyer.

Collins English Dictionary
Insurance Broker (noun): a person or company that is not employed by an insurance company, that finds the best policy for someone who wants insurance.

ADVFN
Insurance Broker:  a broker, independent of any insurance company, who represents the interests of the buyer in searching for insurance coverage at the lowest cost and providing the highest benefit to the buyer.

Cambridge Dictionaries Online
Insurance Broker (noun):  a person or company whose job is to give people independent advice about what insurance is available from different companies and to arrange insurance for them: When you consult an insurance broker, you trust them to find you the policy that best suits your needs.

Farlex Financial Dictionary
Insurance Broker:  A person who sells insurance policies. An insurance broker does not work for an insurance company, but rather represents the buyer of the policy to ensure that he/she receives a fair deal.

Oxford Dictionaries
Insurance Broker (noun):  a person or company registered as an adviser on matters of insurance and as an arranger of insurance cover with an insurer on behalf of a client.

Wikipedia
Broker vs. agent: Though not an absolute separation; an insurance agent is an insurance company's representative by way of agent-principal legal custom. The agent's primary alliance is with the insurance carrier, not the insurance buyer.  In contrast, an insurance broker represents the insured, generally has no contractual agreements with insurance carriers, and relies on common or direct methods of perfecting business transactions with insurance carriers. This can have a significant beneficial impact on insurance negotiations obtained through a broker (vs. those obtained from an agent).