According to Arabic lexicographers, the word Hadith / Hadis means news or new information. In technical terms it is understood to mean the information regarding narrations of Holy Prophet salallahoAlaiheWasalam that may be a part of his lecture of expounded by his actions. Sometimes narrations of sahabah-e kiram that may be a part of their statement or expounded by their actions in the presence of Holy Prophet salallahoAlaiheWasalam, and our Holy Prophet kept silence over that are also called Hadith / Hadis.
Hadith / Hadis is mandatory to perceive the essence of Quran Shareef. For instance, Quransays: establish Salat (aqeemus-salat) but it is silent on the system of performance of this commandment. The methodology of performance of Salat can only be understood fully with the help of Hadith / Hadis. That was the reason why Holy Prophet salallahoAlaiheWasalam had said;
Perform Salat as you see me performing
With this he salallahoAlaiheWasalam established a clear verdict:
Obey the commandment of Allah, which came to us through
Holy Quranby following my traditions.

Hadith / Hadis collections
Types of Hadith / Hadis
Terminology used for books of Hadith / Hadis

Hadith, Hadis