Definition
TRAJECTORY-BASED OPERATIONS (TBO)
An Air Traffic Management method for strategically planning and managing flights throughout the operation by using Time-Based Management (TBM), information exchange between air and ground systems, and the aircraft's ability to fly trajectories in time and space. Aircraft trajectory is defined in four dimensions – latitude, longitude, altitude, and time.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).