third rail

broadly

The electrified rail that runs beside or between train tracks to power electric trains. / (by extension) Anything that is dangerous to come into contact with, or is best avoided.

Japanese Meaning

鉄道の電車に電力を供給するために、線路の隣または間に設置された電化された軌条。 / （比喩的に）接触すると危険で、避けるべき対象のこと。

What is this buttons?

Google Translation / DeepL Translation

車掌は私たちに黄線の内側に下がり、高電圧を通す第三軌条には決して触らないように注意しました。

Details

Sense（1）

The electrified rail that runs beside or between train tracks to power electric trains.

The locomotive third-rail pick up shoes are of the new standard S.R. type. … Whenever the locomotive was working hard there was unmistakable evidence of its higher power than its predecessors in the brilliant and explosive arcing between conductor shoes and the third rail; this was particularly vivid in Quarry Tunnel in the down direction, where the display equalled anything we have seen on the frostiest of nights in an electrified third-rail area.

Google Translation / DeepL Translation