Nanaimo bar means: A chilled dessert confection consisting of a chocolate crumb-based layer, covered by a layer of custard icing, and topped with a layer of smooth chocolate.. It is mainly Canadian English and may not be understood outside that context. 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.