ウェブWord forms: teens. 1. plural noun. If you are a teen, or you are in your teens, you are between thirteen and nineteen years old. Teen is informal for teenager. ティーンエージャー. Most people who smoke began smoking in their teens. 喫煙者のほとんどはティーンエージャーの時に喫煙を開始している. 2. adjective ...