Proprietary trading is a term used in investment banking to
describe when a bank trades stocks, bonds, options, commodities, or
other items with its own money as opposed to its customers' money,
so as to make a profit for itself. Although investment banks are
usually defined as businesses which assist other business in
raising money in the capital markets (by selling stocks or bonds),
in fact most of the largest investment banks make the majority of
their profit from trading activities.