Hadith is a Muslim term that is used to refer to the sayings or acts or ideas of the Prophet Muhammad that are not included in the Koran.
To Muslims, the Koran is, of course, the word of God. However, that does not mean that it is the only source of authority. Instead, the majority of Muslims also believe that it is legitimate to look to Muhammad's life for more information about how they should live and what they should believe. The Hadith help Muslims to understand what the Koran means. It helps them also to know how to apply the ideas of the Koran to their everyday lives. Hadith, then, are sayings and actions of the Prophet Muhammad that can help Muslims have a deeper understanding of what is required of them by their faith.