# What does the symbol for pi with a lower perpendicular mean?

What does mean in context of the equation

• It denotes the Indicator Function en.m.wikipedia.org/wiki/Indicator_function, in your example it returns 1 when $y_i$ equals $y$ and zero otherwise. – xboard Sep 28 '19 at 0:32
• ... with the LaTex code \mathbb{I} giving $\mathbb{I}$ rather than \pi giving $\pi$ – Henry Sep 28 '19 at 0:43

The indicator function $$\mathbb{I}(y_i =y)$$ takes the value 1 when $$y_i =y$$ and takes the value 0 otherwise.

It's not a $$\Pi$$ symbol: you can typeset it using blackboard style: \mathbb{I}.