The BFG is a children’s story by Roald Dahl about a giant — an extremely tall, large man — who is kind. The letters stand for Big Friendly Giant: he is big, but he is friendly, not bad or frightening like most giants in stories. A little girl called Sophie meets him. He catches dreams and blows them into children’s rooms while they sleep. Though actually, a lot of the fun is in the way he talks: he mixes words up into a private, silly English, and children love copying it. The book is the main thing this name points to; there is also a well-known film of the same story. In English you usually say the BFG, and you write it in capital letters because it is a title and a name.