Most prominently used in Lauren Faust's reincarnation of My Little Pony show, Friendship is Magic, and its fans who call themselves bronies. It is a pony-speak for "ladies and gentlemen", or more appropriately, "boys and girls". It is related to somepony, anypony, everypony, etc.
"Fillies and gentlecolts! As mayor of Ponyville, it is my great pleasure to announce the beginning of the Summer Sun Celebration!"
-Mayor of Ponyville, The Mare in the Moon pilot episode.