Though we typically use the term broker to describe the professionals who buy and sell stocks, other, less widely recognized titles are actually describing the ways securities change hands and all the people who get the job done.

Brokers:

Handle buy and sell orders placed by individual and institutional clients in return for a commission.

Dealers:

Buy and sell securities for their own or their firm's account rather than for a client.

Investment Bankers, or Underwriters:

Buy new issues of stock directly from corporations and sell them to individual and institutional investors.

Traders:

Buy and sell securities for their own portfolios. In this sense, the term is interchangeable with dealer.

However, the term traders is also used to describe employees of broker-dealers who handle securities transactions for the company and its clients.