The term refers to lesbians, usually young ones. The term became popular in Japan during the 70's and 80's due to a 70's Japanese magazine that called lesbians “the lily tribe” causing the lily flower to be
associated with
lesbianism.
During the early 2000's when anime and
japanese culture became more accessible, the term begun to be used in other countries, but to this day, it is still used majorly in Japan.