"alternative cannabinoid" is slang related to drug use: any psychoactive cannabinoid that is synthetically or semisynthetically derived from delta-9-thc and is not naturally present in cannabis except in negligible amounts. If your teen uses it casually, it does not automatically mean they are using; many young people repeat drug slang they see in song lyrics, memes, or films without first-hand experience. However, repeated, context-specific use (talking about scoring, prices, plans for the weekend) is worth a calm, non-confrontational conversation. Ask open questions rather than reacting to the word itself, and check what they actually know about the substance.