P

paladin
paleogamer
paleotaku
paper-thin walls
Paranoia
Pardue
party
party cohesion
Path of Sticking-My-Thumb-Up-My-Ass, The
Path of What-I-Was-Going-To-Do-Anyway, The
patzer
PBM
PBW
PC advantage
PC halo
Pedo mellon a minno
pen and paper game
Penn Gillette's Law
People are pointing and screaming.
percentile dice
period
phantom ghoul
phase, to
Phil Moscowitz
piker
pimp, to
ping
Pizza Monkey
pixel bunny
PK
player character
player revolt
plop, to
plot breaker
plot device sticker
point juggling
point system
poke, to 
PokéMom 
Pokémon
Polydichloric Euthimal
polyhedral dice
polymorph, to
pool
power gamer
power-up
pre-rolled character
Prophetess, The
pseudo-dragon
psionics
Psycho Christian
pull, to
-punk
Purina Human Chow
pwned