Railings means: The standard British English plural for a fence or barrier made of rails or metal bars - the kind that lines streets, parks, and the fronts of townhouses. In Britain, 'railings' is the normal term. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.