How is the negative binomial the inverse of the binomial distribution?

[Simfish]

Can anyone give a user-friendly explanation?

http://en.wikipedia.org/wiki/Negative_binomial_distribution#Properties

We see that the binomial distribution measures the probability of X successes after n trials, whereas the negative binomial measures the probability of the trial number after the Xth success. The question is - how does this relate to an inverse? How would the word "inverse" simplify the analogy?

 

[EnumaElish]

It is not an inverse in the usual sense that g^-1(g(x)) = x.