In Australia, it specifically refers to a young woman dressed up for the Spring Racing Carnival in Melbourne. Additionally, it is usually only used in the plural form.
It is taken from the term for a young female horse before she is old enough for racing.
2. "Check out those fillies in The Birdcage!"
noun, plural: -lies
Typically refers to 13-30 year old female fans of the 2010 reboot of the show My Little Pony: Friendship is Magic. Similar as, but not to be confused with: "brony" (bro+pony) which is more often used for the male equivalent. It is a well-known and undisputed fact that bronies are on average about...20% more awesome due to their rarity.