Math Help - Physical meaning of imaginary term

1. Physical meaning of imaginary term

Hello
In the following integral which I obtained from Wolfram, what is the physical meaning (e.g. in a heat conduction problem) of $\sqrt{-\sinh^{2}(bx)}$.
Thanks.

$\int\frac{dx}{\cosh^{3n+1}(bx)}=\frac{\sinh(bx)\co sh^{-3n}(bx)}{3nb\sqrt{-\sinh^{2}(bx)}}\,_{2}F_{1}\left(\frac{1}{2},-\frac{3n}{2};\frac{2-3n}{2};\cosh^{2}(bx)\right)$