‘Ḥadīth’ means ‘speech’ in Arabic. Technically, it indicates a report or a body of reports (the Arabic word is used both ways, although there is also a plural, aḥādīth) of what the Prophet or some other authoritative teacher said. From hadith, Muslim jurisprudents infer the Sunnah, the pattern of behaviour that Muslims should follow. A hadith report normally comes in two parts, the matn (‘main part’), which is what the Prophet or other authority said, and the isnād (‘support’), the chain of authorities by which it has reached the present collector. The isnād is one's proof that this report was not made up somewhere along the way and projected backward onto a venerable authority of the past. In time, writers distinguished between ḥadīth going back to the Prophet and āthār (sing. athar) going back to other early Muslims, but the terms were interchangeable in the early centuries. (Hadith reports were once called ‘traditions’ in European languages, by analogy with preliterary oral reports of what Jesus said. ‘Hadith’ is now in standard English dictionaries, but ‘traditionist’ may still be used for someone who collects hadith.)

Here is another (henceforward, ‘there related to us’, ‘from’, and so on will be abbreviated by a simple sign):

The above are from two of the most trusted Sunni collections of hadith. Here is one from a collection of weak hadith: