"Jello salad" means: A salad made with flavored gelatin (often of the Jello brand), fruit or vegetables, and other ingredients such as cottage cheese, cream chee.... 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.