A weighted vest is a wearable fitness vest with added weight, used during walks and workouts. Currently trendy on wellness TikTok. Not concerning, generally safe; check pediatric guidance for teens. If your kid uses it constantly, ask them where they first heard it, not to police their speech but to understand which online community they are in. Most slang of this kind moves through TikTok and group chats, so seeing it in your child's vocabulary just means they are plugged into normal teen internet culture.