The term was coined by Gifford Pinchot III in the late 1970s. When describing intrapreneurial employees, he often refers to “dreamers who do” : people, who take hands-on responsibility for innovation within a business. Sometimes that means bringing their own ideas to life, but more than often it means finding pathways for existing ideas within the organization and turning them into profitable businesses. In that sense, intrapreneurs do for corporate innovation what an entrepreneur does for her startup. See also this nice article from the Corporate Rebels for more information.
Pinchot, G. I. (1985). Intrapreneuring: Why You Don’t Have to Leave the Corporation to Become an Entrepreneur (1st edition). Harpercollins.