Ply(x) for any non-negative integer x is defined as follows:
Ply(0) = 0
Ply(x+1) is the smallest positive integer greater than Ply(x) such that li(Ply(x+1))-Ply(x+1))>0 and li(Ply(x+1)+1)-Ply(x+1)+1)<0 where x) is the prime counting function of x and li(x) is the logarithmic integral of x.
The name is a combination of "pi" and "li".
The -ply suffix can mean the Ply function of the original number, so Googolply = Ply(10^100) for example