Something that is on the Internet is said to be "online."
The Internet is an amorphous interconnection of countless servers and computers across the telecommunications grid. Being online, therefore, yields enormous added potential for human interaction and commerce.
Investing online refers to using an online stockbroker, such as Sharebuilder.com or Scottrade.com. An online investor may also get much of his information online, from the websites of established pre-internet companies, such as Dow Jones, or from online companies like Yahoo!, which provides free financial information at Yahoo Finance.