The capital Greek letter Pi ($Π$) is used in math to represent the product operator. Typically, the product operator is used in an expression like this:
The product operator has three parts: the initial index variable value, the end value, and the expression being multiplied together. In plain language, the above expression means starting with $i=0$, substitute the value of $i$ into the expression $i+1$ to get a subexpression. Increment the value of $i$ by adding one to its current value and substitute the value of $i$ into the expression $i+1$ again to get the second subexpression. Repeat this process until the value of $i$ reaches the end value $2$ and then multiply the resulting subexpressions together.
Symbol  Format  Data 

Π  Unicode 

$Π$  TeX 

SVG 