An individual or organisation acting as an intermediary in a transaction, typically on behalf of one of the parties in return for a fee or commission. The term is used in a number of fields, including investments, share trading, insurance and real estate. A stock broker, for example, will execute ‘buy’ and ‘sell’ stocks & shares orders on behalf of an investor. An insurance broker, by contrast, will advise on and negotiate insurance products on behalf of a client.