From a 2011 review of Daniel Kahneman's Thinking, Fast and Slow - which, as I've written before, is very good:

But intellectual influence is tricky to define. Is it a matter of citations? Awards? Prestigious professorships? Book sales? A seat at Charlie Rose's table? West suggests something else, something more compelling: "Kahneman's career shows that intellectual influence is the ability to dissolve disciplinary boundaries."

That's a pretty compelling definition to me.