- Oxygenation
- Oxyhydrogen
- Oxylipins
- Oxymatrine
- Oxynitride
- Oxysterols
- Oxytocin
- Oyster
- Oz
- Ozone
- Ozone cracking
- Ozone layer
- Ozone monitor
- Ozone-depleting
- Ozonides
- Ozonolysis
- P systems
- P vs NP
- P waves
- P-adic analysis
- P-anisidine
- P-chart
- P-code
- P-complete
- P-coumaric acid
- P-cresol
- P-cycle protection
- P-cymene
- P-glycoprotein
- P-hacking
- P-loop
- P-n diode
- P-n junction
- P-selectin
- P-site
- P-space
- P-toluenesulfonic acid
- P-type
- P-wave modulus
- P-waves
- P-xylene
- P120
- P120 catenin
- P16
- P2
- P21
- P27
- P300
- P38 mitogen-activated protein kinases
- P3P