Tone is an attitude that the author conveys through writing about an audience or subject. Tone is typically expressed through word choice or through the viewpoint the author has on a particular subject.
All written pieces contain a main subject, the central theme of the piece. The manner in which that theme is expressed is called tone. In literature, in particular, tone is used to represent the author's attitude towards a specific subject. Tone also helps readers determine how they should be feeling while reading a piece and helps shape the readers' views of character personalities and differences. It lends color and depth to a written piece.