They named the project Phil because it sounded friendly. (For those who required an acronym, they had one handy: Probabilistic Hierarchical Inferential Learner.) That was bad news for a Google Engineer named Phil who kept getting emails about the system. He begged Harik to change the name, but Phil it was.
– Steven Levy, In The Plex: How Google Thinks, Works, and Shapes Our Lives.
How does Google decide which Adsense advertisements to show on which Web pages? How do they avoid showing inappropriate advertisements on those content pages? How does the document classification system they use to power those decisions work and has its use been expanded beyond Google’s advertising system?