1) A Fairy, is an Ethereal being with, like has already been said, the ability to communicate with all aspects of nature and their surroundings. Using animals and insects to transport them like we use horses, and ostriches in Africa, and such like.
2) Yes, their existence is yet to be confirmed by science and never will be, but they DO exist. A childhood story has a basis in reality, Dragons, Unicorns, Goblins, Ogres and Trolls. All have once existed, but adults can't believe in something that they have been told is fantasy by their parents before them, once a child has absorbed all the fantasy, his or her parents wait until the child is 5 or 6 years of age and then, they say " sorry, they never existed". From that point the child's "Fantasy" slips away and blends in to the fact...The child loses their ability to connect with their world, the world of Fantasy, magic, Dragons, knights and Ogres. Their are things in heaven and earth that are stranger than our own imaginations. Imagination, the ruin of our once incredible childhood world...Imaginary Friends?