What some newspapers call companies who do business over the internet. It's obviously supposed to be based around the choice of tld, but in their excitement to make things look techy, the journalists didn't notice that dot.com is pronouced dot-dot-com, which is just silly.
This, along with other terms such as dotcom, new media and information superhighway, is a symptom of journalists (and others) not being sure of how to handle the internet.