Piano Shaped Object - a third-rate or worn-out piano; a piano brand scorned by technicians and tuners

Phantasy Star Online - a video game

Phonic Sonic Oradea - electronic music community of Oradea

Protocol Support Organization - one of the three initial components of ICANN, later disbanded

Phone sex operator - a person who provides phone sex service

Particle Swarm Optimization - a swarm intelligence optimization technique

Pittsburgh Symphony Orchestra

Penalty shootout - a method of determining a winner in sports matches which would have otherwise been drawn or tied

Pakistan State Oil

Public Service Obligation - a form of state subsidy for transport links which are not commercially viable

Phase-shift oscillator - an electronic circuit that generates sine waves

Paysite operator - the owner/operator of a paysite