A trip is the act of travelling from point A to point B with no transfers (a single trip).
A journey on the other hand can be one or a number of trips (transfers) combined to make it from point A to B. When making a number of trips to get to your destination it is still one journey if you touch on within 60 minutes of touching off on your previous trip.
Please note - discounted fares do not apply to an Airtrain journey.
Journey
A journey is the distance travelled from the origin to the final destination. A journey might involve several trips using different transport modes. The sum of these trips will make up one journey.
Trip
A trip is defined as the distance travelled from point of embarkation on a vehicle (or vessel) to its terminus, or to a location, prior to the terminus, where the passenger disembarks from the vehicle. A trip may be the full journey or part of the journey.