Used when a child character has notably adult-sized breasts, but otherwise retains their child-like proportions. As a good rule of thumb, use the number of heads tall the character is to decide if they rank as an oppai_loli or not. Also note that some oppai_loli pics still need the loli tag, but not all.
If you are not sure whether or not a post should be tagged as loli, ask in the loli/shota check thread.
This tag implicates breasts (learn more).