This is an arcane quantity that is the integral of the power four of the variable times it's probability. I really thought that was the interviewer trying to empress me with HIS knowledge (he has masters in statistics). Since Curtosis is not used much in physics, chemistry or in anything else. Indeed, to quote "Statistics" by Barlow: "It is really an obscure and arcane quantity whose main use is inspiring awe in demonstrators, professors, or anyone else you need to impress" Page 14. So take that the way you want.