"Black Saturday" means: February 7, 2009, a day of devastating bushfires in Victoria, Australia, which killed 173 people.. This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.