It's pretty difficult to Google for the meaning of a formula.
This is the equation, it has to do with ellipses and GIS coordinates.
$$\nu =\frac{ a} {\sqrt{(1 - (e^2 \cdot \sin(\varphi))^2)}}$$
$a$ is an ellipsoid axis.
$\varphi$ is geodetic coord latitude in radians.
$e^2$ is eccentricity squared.
I see it all over the code I'm porting and would like to separate it out but I can't figure out what to call the function!
Edit: On page 38 of this PDF the equation and its context is described.