A junction was a crossing of maintenance shafts aboard a starship.
In September 2152, T'Pol and Malcolm Reed had to deactivate the warp engine from a panel in junction 42-A. (ENT: "The Catwalk")
In 2153, two Borg-assimilated Tarkaleans managed to sabotage the avionics control system located in maintenance shaft C junction 12 aboard Enterprise NX-01. (ENT: "Regeneration")