Chap lau chu means: A ten-storey housing flat built by the Singapore Housing and Development Board (HDB) in the 1960s (now mostly vacated).. It is mainly Singaporean 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.