Voxyde covers what dot product is and how to use it in Houdini.
This new tutorial from Voxyde covers everything you want to know about using dot products, specifically in Side FX Houdini.
A dot product is a vector operation that compares two values and outputs a float value that can specify the differences between the two angles compared. For example, the two values Voxyde uses are a vector and a normal in Houdini.
After explaining how the Dot Product works, the tutorial covers a few examples of using it.