It's anyone's guess!
Acronym Definition
OPP Opposite
OPP Opportunity/Opportunities
OPP Ontario Provincial Police (Ontario, Canada)
OPP Office of Polar Programs (National Science Foundation)
OPP Office of Pesticide Programs
OPP Object Push Profile (Bluetooth)
OPP Office of Pollution Prevention
OPP Over Power Protection
OPP Opper (adjudant-onderofficier; Dutch)
OPP Omega Psi Phi (Fraternity)
OPP Office of Physical Plant (Pennsylvania State University)
OPP Orleans Parish Prison (Louisiana)
OPP Oriented Polypropylene Film
OPP Organizational Process Performance (process area)
OPP Outline Planning Permission
OPP Ovine Progressive Pneumonia (Montana sheep pneumonia)
OPP Other People's Property
OPP Organophosphate Pesticide
OPP Other People's Problems
OPP Office of Policy and Planning
OPP Operational Planning Process (Canada)
OPP Organophosphate Poisoning
OPP Osteopathic Principles and Practices
OPP Opening Price Point
OPP Order Processing Pipeline
OPP Ore Processing Plant (mining extraction)
OPP Original Prose and Poetry
OPP Office of Program Performance (Legal Services Corporation)
OPP Off-load Preparation Party
OPP Opposed/Opposite
OPP Orinda Park Pool (California)
OPP Other People's Parts
OPP Option to Purchase Paid-Up Additions (optional insurance rider used to increase life insurance benefit)
OPP Off-Peak Power
OPP Other People's Privates
OPP Official Party Poopers

OPP FCC Office of Plans & Policy
OPP Oregon Patriot Party
OPP Octal Print Punch
OPP Order Processing Point
OPP Out of Print at Present
OPP overprotective parent(s)
OPP Organic Pear Production
OPP Optional Program Product(s)
OPP Ontario Paintball Place
OPP Organizational Placement Process
OPP Office of Patent Publication
OPP Obligation Phasing Plan
OPP Orthogonal Polynomial Predistortion
OPP Organization and Personnel Plan
OPP Operation Process Plan
OPP Oral Proposal Planner
OPP Optical Path Protection
OPP Oxley Park Primary (school)
OPP Outcome Project Plan (Canada)
OPP Open Promenade Position (dance)
OPP Off Plan Property (various locations)
OPP Oxygen Partial Pressure
OPP Out-of-Pocket Payment (insurance)
Or something else...