Plain English Meaning
A licensed aircraft mechanic who is legally allowed to work on airplanes and sign off that the work was done correctly so the airplane is safe to fly again.
Full Definition
An FAA-certificated mechanic authorized to inspect, service, repair, and approve for return to service civil aircraft and aircraft components, in accordance with the privileges and limitations of their certificate and ratings (typically Airframe and/or Powerplant) under 14 CFR Part 65.
Context Anchor
In the section, the term appears because a mechanical problem should be by a , not worked around by unsafe starting methods.