Initialism of parts per billion.

(economics) Initialism of production-possibility boundary.

Initialism of parts per billion.

(sciences) parts per billion by volume

(physics) proton and antiproton (used attributively to describe a collision or other interaction of these two particles)

(aviation, travel) Positive Passenger Bag Match. An airline system used to ensure that baggage is not loaded on an aircraft if the passenger does not board.