Career capital is the stock of resources that increase the future impact of a person's career. It consists of skills, connections, credentials, and runway.
According to 80,000 Hours, building career capital is one of the most effective ways for individuals to have an impact over the course of their careers. This is especially the case for individuals at the beginning of their careers, since the value of this capital is roughly proportional to the remaining duration of a person's career. In addition, 80,000 Hours used to recommend building flexible career capital—skills, connections, and credentials useful across a wide variety of jobs—to individuals uncertain about their careers, though more recently they have de-emphasized this recommendation, stressing instead the importance of career capital that is most useful in the highest-impact jobs.
Todd, Benjamin (2015) What should you look for in a job? Introducing our framework, 80,000 Hours, July.