permanent head damage :-)))

Acronym Definition
PhD Philosophiae Doctor (doctor of philosophy)
PHD Presbyterian Hospital of Dallas
PHD Portable Hard Drive
PHD Post Hole Digger (construction)
PHD Prolyl Hydroxylase (protein)
PHD Pleckstrin Homology Domain (biochemistry)
PHD Plant Homeodomain (microbiology)
PHD Port Hueneme Division (US Naval Surface Warfare Center)
PHD Permanent Head Damage (slang)
PHD Push Here Dummy (point & shoot cameras)
PHD Professional Help Desk
PHD Probability Hypothesis Density
PHD Pulse Height Distribution (ion detection)
PHD Personal Hemodialysis System (Aksys, Ltd.)
PHD Pacific Health Dialog
PHD Phenomena in High Dimensions
PHD Portable Handheld Device
PHD Post Holiday Depression
PHD Pre-Hearing Detention
PHD Plumbing Hardware Dispatcher (Google TiSP spoof)
PHD Process Historian Database
PHD Pisarenko Harmonic Decomposition
PHD Player Hater Degree
PHD Punjab Haryana and Delhi (India)
PHD Phase History Data
PHD Process Hierarchy Diagram (business process modelling)
PhD Poor Hungry Doctor
PHD Parametric High Definition
PHD Port Huron & Detroit Railroad
PhD Pothole Dodger (driver on poorly maintained roads)
Phd Pathfinder Healthcare Developments (Smethwick, West Midlands, UK)
PHD People Helping the Disabled (Edmonds, Washington)
Phd Post Homicidal Depression (serial killers)
PHD Production Hole Diameter
PHD Praising Him Daily
PHD Public High Diploma
PHD Pray Hard Daily
PHD Psychology and Human Development (various organizations)
PhD Piled High in Debt
PHD Poly-Harmonic Distortion
PHD Phased-History Data