According to the Third Doctor, a Faraday cage was a framework of conducting materials that blocked electrical fields. Anything inside the bunker would be shielded from external electromagnetic radiation, and also cut off from possible detection.
The Doctor explained to Sarah Jane that they used small ones in the UNIT lab to screen out electromagnetic inference. This effect was also why portable radios did not work in lifts. (PROSE: Generation Gap)
The Seventh Doctor theorised that the Klickliqhter was acting as a Faraday cage, conducting all temporal magnetic discharges around its shell, and leaving its interior entirely untouched. (PROSE: The Hunting of the Slook)
As the Tenth Doctor and Lady Christina discovered, the 200 bus acted as a Faraday cage, a great box of metal protecting them from the wormhole they drove right through. Nathan elaborated that in a thunderstorm, the safest to be was in a car, because the metal would conduct the electricity right through. The Doctor told them both that there were different dynamics involved with wormholes, but the concept was the same. (TV: Planet of the Dead)
The Drum contained a Faraday cage that was also lined with lead to shield against radiation. The crew of the base sheltered inside the cage when the ghosts appeared, as the ghosts could not penetrate it. Later, the Twelfth Doctor organised the crew to trap the ghosts inside the cage. The ghosts later escaped, but the Doctor used a hologram of himself with a recording of the call of the Fisher King to lure the ghosts back inside and trap them. Once they were inside, he contacted UNIT to deal with them. According to the Doctor, UNIT will cut the Faraday cage out of the base and eject it into space. Once far enough away from the Earth's magnetic field, the ghosts inside the cage will dissipate. (TV: Under the Lake / Before the Flood)
The Drum's Faraday cage was so effective at blocking EM fields, it was even able to prevent a signal reaching Clara Oswald's augmented superphone, despite it having the ability to contact the Doctor across time and space. (TV: Before the Flood)