Definitions

On-the-job training instructor (OJTI) - a rated air traffic controller with an air traffic control licence endorsed with a current qualification that permits the holder to carry out instruction in the operational environment for which the rating is issued.

Source: European Manual of Personnel Licensing - Air Traffic Controllers

On-the-job training instruction - the phase of unit training during which previously acquired job-related routines and skills are integrated in practice under the supervision of a qualified on-the-job training instructor in a live traffic situation.

On-the-job training instructor (OJTI) endorsement - the authorisation entered on and forming part of a licence, indicating the competence of the holder to give on-the-job training instruction and instruction on synthetic training devices

Source: EU Regulation 2015/340