I am reading a piece of a physic paper where a function is mentioned without being given a name or reference - I guess it is a canonical one and that I should be familiar with.
The expression goes as:
$$|_2F_1(a,b;c;z)|$$
with $a,b,c \in {\mathbb R}$ and $z \in {\mathbb C}$. Also I am fairly sure the lowerscript 2 is a label on the function.
On
In mathematics, the Gaussian or ordinary hypergeometric function 2F1(a,b;c;z) is a special function represented by the hypergeometric series, that includes many other special functions as specific or limiting cases. It is a solution of a second-order linear ordinary differential equation (ODE). Every second-order linear ODE with three regular singular points can be transformed into this equation.
This is probably the hypergeometric function.