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")