Lexically speaking, the word “hadith”, whose plural is ahadeeth is, New, recent, existing newly, for the first time, not having been before… Information, a piece of information, intelligence, an announcement… a thing, or matter, that is talked of, told, or narrated.
In both the Quran and hadith, the word has been used in reference to a religious communication, a story of a general nature, a historical story and a current story or conversation.
As a technical term, a hadith is basically any report of the Messenger of Allah’s (peace be upon him) saying, action, tacit approval, manners, physical characteristic or biographical data. In other words, it is any report about the “sunnah,” as defined by the scholars of hadith.
Every hadith is composed of two parts:
(a) isnaad, or chain of authorities, and (b) matn, or the actual text of the hadith. Both of these parts have to meet stringent requirements for the hadith to be accepted and considered true.
In general, one can divide all hadith into five basic categories:
(a) sahih or authentic hadith;
(b) hasan or “good” hadith;
(c) dhaeef or weak hadith;
(d)dhaeef jiddan or very weak hadith and
(e) maudhoo or fabricated, forged hadith.
Actually, these can be broken down into two even more basic categories: accepted hadith (sahih or hasan) and rejected hadith (dhaeef, dhaeef jiddan and maudhoo).
To be a source or authority of Islamic law, a hadith must be from the categories of sahih or hasan. In order for a hadith to be sahih or hasan on its own merit, it must meet the following five criteria:
(1) The chain or isnaad must be unbroken. In other words, each source must have received the hadith directly from the one on whose authority he is relating it all the way back to the Prophet (Peace be upon him). If there are any missing authorities, the chain would be considered broken and unacceptable.
(2) Every narrator in the chain must be of acceptable righteousness and character; in other words, each narrator must be morally fit. Impious people are not accepted for then impiety is a sign that they do not fear Allah and, hence, they cannot be trusted to take extreme care in narrating the statements of the Prophet (Peace be upon him). If just one narrator in the chain docs not meet this criterion, the hadith will have to be rejected.
(3) Moral characteristics are not sufficient. Each narrator must also be proficient and exact when it comes to narrating hadith. If a person is known to make lots of mistakes when narrating hadith, either from his memory or from his writings, his hadith will not be accepted.
(4) Both the chain and the text of the hadith must be such that they do not contradict what has been narrated through stronger means.
(5) Upon inspection of the different ways a hadith is narrated, it must be the case that no mistake or defect is spotted in either the chain or the text of the hadith.
If any of these conditions are not met, the hadith will be rejected as either weak (dhaeef) or very weak (dhaeef jiddan), depending on the magnitude of the weakness. Hadith which are graded dhaeef or weak may be raised to the level of Hasan if sufficient corroborating evidence is found for them. Hadith which are dhaeef jiddan may never be raised because the nature of their weakness prevents them from being considered as supporting evidence or as being supported by other similar evidence. Of course, fabricated hadith are in a different category completely and would never, under any circumstances, be considered an authority or acceptable in Islamic law.
 A strict transliteration of the word would actually be hadeeth. However, It has become well-known and pronounced correctly as hadith; hence, this author leaves the word as hadith In all of his writings, except in the transliteration of Arabic titles. Furthermore, this author prefers to use the word hadith for both the singular and the plural, like the word deer in English, rather than the Arabic plural ahaadeeth,
 Lane, vol. 1, p. 529
 Cf, Mustafa Muhammad Azami, Studies in Hadith Methodology and Literature (Indianapolis, W: American Trust Publications, 1977), pp. 1-2.
 There are two other important terms that are closely related one is khabar and the other is athar. The word khabar literally means “a report, news.” It is used by some scholars of hadith as a synonym for hadith. However, others use the word hadith for what is attributed to the Prophet (Peace be upon him) and what is attributed to other than the Prophet (Peace be upon him) would be called khabar. Hence, a person specializing in the sunnah is called a muhaddith while someone concerned with history and other narrations is called Ikhbaari. Al-Suyooti notes that when the word “hadith” is used by itself, without any additional adjective describing its source, it should only be used in reference to hadith of the Prophet (Peace be upon him). Athar literally means the remnants or remains of something. Technically, it is used for what is narrated from the Prophet (peace be upon him), his Companions, their followers and other early scholars. A person who studies these reports and follows them is referred to as athari. Al-Suyooti says that athar should be used only for what is narrated from the Companions and the Followers and not for what comes from the Prophet (Peace be upon him), which should be termed hadith. Cf., Muhammad Dhiyaa al-Rahmaan al-Adhami, Mujam Mustalahaat al-Hadeeth wa lataaif al-Asaaneed (Riyadh: Adhwaa al-Salaf, 1999), pp 8 (for atbar) and 148 (for khabar); Muhammad al-Manshaawi, Qaamos Mustatahaat at-Hadeeth al-Nabawi (Cairo: Daar al-Fadheelah, n.d.), pp. 16 (for atbar) and S6 (.tor kbabar).
 A fabricated or forged hadith is one which can be traced to an actual fabricator of hadith. When discussing hadith, many scholars do not even consider it a type of hadeeth.
 This brief introduction Is not meant to be extensive or detailed. The Interested reader should consult this author’s “Sahih Hadith,” al-Basheer (Vol. 3, No. 4, Nov.-Dec. 1989).