What is "Py" in Ray casting terminology?

Question

I am followin this tutorial for doing a ray casting tutorial with python and pygame. But the problem is that in the algorithm for checking intersections in the grid he uses an abreviature never explained before("Py") I first thought that was the number pi but it isn't.

Can anynone who has done this tutorial or know the raycasting concept explain me what it is? Thanks!

Answer 1

Py is the y coordinate of the point P. This is shown in the diagram at the top of the page where it says P (Px, Py).