What is the meaning of the subscript in the polygamma function?

[rman144]

So I've been working on a proof and Wolfram Alpha gives the following partial sum formula for one of the summations in the proof:

http://www.wolframalpha.com/input/?i=sum[e^(-(2k+1)/x)/(1+e^(-(2k+1)/x)+)^2+]

What does the terminology involving psi mean? I think it is the first derivative of the polygamma function, but I don't understand what the subscript e^(2/x) means.

Thanks in advance for the help.

 

[CRGreathouse]

I don't know what that subscript means either. It's funny that W|A thinks that it needs to tell you what the natural logarithm is but not the (variant of the) trigamma function.