A mechanic is a person who uses tools to maintain, repair and build machinery.
History and specifics
When Captain Atish Khatami was confronted by Lieutenant Ming Xiong in the corridor of the USS Endeavour (NCC-1895) about a Starfleet Intelligence mission, she immediately dragged him into a maintenance bay to talk in private. Two enlisted mechanics were currently welding in the room and quickly vacated it when Atish ordered them out. (VAN - Declassified novella: The Stars Look Down)