Neuk means: A corner; a nook. A fairy fiddler frae the neuk, [nook] - "Robert Burns", by William Allan Neilson (1917).. It is mainly Scottish 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.