Unicorns are horses with horn's. They are said to have magical powers and are usually teamed up with rainbows and butterflies. In Hortan hears a Who a girl says that in her world everyones a unicorn.
In the show My Little Pony: Friendship is Magic, there are alot of unicorns, mostly in Canterlot. Also, there are 2 main characters that are unicorns and they are Twilight Sparkle and Rarity.