Intonation (speech)

Intonation is about the variation in pitch of speech which may change meaning. How something is said may change its meaning. All spoken languages use this tactic.
The study of intonations is part of prosody.
A simple example which shows how important prosody is. A parent says to a child "well done". Without some annotation, one can't decide whether the child has indeed done well, or whether it has {say} knocked a glass of milk over.