Originally a trader in stocks and shares. Stockjobbers started transacting business in coffee houses and later used the Royal Exchange. In 1773 the Stock Exchange replaced these venues and stockjobbers were differentiated from stockbrokers in so far as the jobber was made effectively a wholesaler in stocks and shares. He bought from and sold to stockbrokers only, and they then acted as agents for the general public. Jobbers still exercise this function, but with the reorganization of the Stock Exchange, completed in 1986, the distinction between the jobber and the broker has become less important, as traders will be permitted to act in both capacities.
Even under the new order stockjobbers as such will still exist, as some firms may prefer to act in one capacity only and will restrict their business to that of market maker. This is particularly likely in the case of firms which have previously tended to specialize in certain types of shares. As market-makers, jobbers traditionally quote a double price – a price at which they will buy and a price at which they will sell. The difference between these prices is known as the ‘jobber’s turn’. The distinction between jobbers and brokers in stock market dealings is a peculiarly British phenomenon.
Reference: The Penguin Business Dictionary, 3rd edt.