A railing or rail was a long bar that protected against falls from high heights. The most common use of railing was the handrail, which was a support bar used for resting one's hands on in instances such as climbing a set of stairs.
In 2151, Trip Tucker noted that if one were to rest one's hands on the handrail of a lift in Enterprise NX-01's engineering section during the lift's operation, one's fingers might be amputated. (ENT: "Unexpected")
In 2152, Trip Tucker sarcastically offered to polish all the handles and rails in Enterprise NX-01's Engineering while the ship unexpectedly changed course for the Pernaia system. After Jonathan Archer gave him a look, he decided to purge the impulse reactors instead. (ENT: "The Seventh")
In 2369, Quark berated Rom for returning a patron's full currency pouch, giving him the punishment of polishing every rail in Quark's. Soon after, spying a lazy Nog, Rom passed on the punishment to him. (DS9: "The Nagus")
In 2399, a Romulan death squad operated near the Starfleet archives in San Francisco but inexplicably did not show up on the security feed. Later, director of Starfleet Security Commodore Oh looked at the footage and wondered if she recognised disruptor fire relected in a handrail. (PIC: "Remembrance", "Maps and Legends")