Intonation is the word for the melody of spoken language. The way the musical pitch of the voice rises and falls. Intonation systems in languages are very complicated and difficult to analyse and linguists disagree about how English intonation works.
One was in which intonation seems to be used is to show how a piece of information fits in with what comes before and after. For instance, a speaker may raise his or her voice when taking over the conversation from - somebody else or to indicate a change of subject. A rise or fall on a particular word show that this is the centre of the message – the place where the new information is being given or it may signal a contrast or a special emphasis. When a speaker ends – on a falling tone, this often express uncertainty, suggest that there is more to be said or invite another speaker to take over.
Intonation (together with speed, Voice quality and loudness) can also say things about the speaker’s attitude. For instance, when people are excited or angry they often raise and lower their voices more.