Loli (EntityClass, 5)
From Compile Worlds
A loli, fully known as lolita, is a young girl typically underage and with no tits. There are, however counterexamples of both of these characteristics, such as Izumi Konata (who turns 18 during the anime series, but is still a loli) and Minamoto Chizuru (who tends to smother her disapproving crush in every freaking episode).
There are a vast number of personalities associated with lolis, including magical girls, catgirls, Kid Heroes (In the case of girls) and tsundere.