"K-hole" is slang related to drug use: the state of dissociation from (and lack of control over) the body commonly experienced after taking relatively high doses of the drug ketamine. 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.