The capital Greek letter Pi (\Pi) 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 sub-expression. 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 sub-expression. Repeat this process until the value of i reaches the end value 2 and then multiply the resulting sub-expressions together.