“Tone” is the writer’s attitude that is expressed in the writing.

For example, the tone of a novel could be suspenseful, because the author holds back certain information to create this feeling.

Tone is also generally thought of as describing the work as a whole, rather than a particular section.

While “tone” is the writer’s attitude, “mood” is the feeling the reader gets from the writing.  Tone often describes the writing overall, but the mood of a piece of writing can change throughout it.  For example, at the death of a character, the mood could be depressed or sad, but at the discovery of a long-lost friend, the mood could be upbeat and joyful.  A reader's mood often goes hand in hand with characters, if the character-reader relationship is strong enough.