Maktub is an Arabic word for "it has been written (it's destiny)." It's the title of a book by Paulo Coelho.
Antonio Gonzalez, a real 15 year old with cancer, inspired the character in the movie.
Brazilian writer Paulo Coelho's influence is recognized in the word used for the title "Maktub" and in a copy of "The Alchemist" playing a role in the story. In most of Latin America the title is "Cambio de Planes" (Change of Plans).