10/14/15 - There have been updates, but no notifications! Here's a notification! Around 40 "pig_girl" images added.
Girls made of goo or slime, but keeping a definite shape. slime is more amorphous, and used mainly for monsters, whereas goo will almost always look like a girl. A subset of monstergirl.
goo is broken down further by color, i.e. blue_goo