Underage

Underage 

Refers to stories featuring at least one main character below the age of majority (be it 16yrs, 18yrs, or 21yrs depending on author and country of origin) whom engages in a romantic or sexual relationship, whether with another underage character or a recognized adult. The characters who are technically minors usually consent willingly to the relationship in such stories, but the fics may contain non-con/rape and abuse as well so watch for warnings.