A lightning rod was a piece of metal designed as a conductor to attract and direct lightning into the ground. This would prevent damage to structures or individuals.
An effort in 2368 to remove dust and volcanic ash from Penthara IV by attracting it to the USS Enterprise-D and discharging it harmlessly into space was likened to turning the Enterprise into a lightning rod. (TNG: "A Matter Of Time")
In 2377, when USS Voyager was brought back into temporal sync following a chronokinetic surge that had shattered it into 37 different timeframes, Commander Chakotay had Lieutenant B'Elanna Torres reroute power main power to the deflector dish and setting the polarity to a specific frequency, stating "Have you ever heard of a lightning rod? In about three seconds, we're going to need one." (VOY: "Shattered")