railing noun [C usually plural] a vertical, usually metal or wooden post, which is used together with other such posts to form a fence: Tourists pressed their faces against the palace railings. (from dictionary.cambridge.org)
Strange. I hadn't thought of a fence as railings. I accept that sentence, but as my illustration shows, I think of a railing as something to hold on to when using stairs. I wonder if the British use the plural even in the case of stairs.
I'd call it a railing if it were about waist-height. If it were taller, it would be "a fence." I think of railings at things that keep you from falling, but fences to keep you from entering. Or leaving, I guess, if you're in jail.