Question: What is a hadith?

Answer: Saying of the Prophet  

Question: What is a chain of transmission?

Answer: A chain of narrators who relate a hadith from the Prophet or the Ahl al-Bayt (as)

Question: What is a sahih hadith?

Answer: Authentic, reliable hadith

Question: What is a weak hadith?

Answer: A hadith that has a questionable chain of transmission, like a liar among its narrators

Question: What are the major compendiums of hadith in the Shia Muslim world?

Answer: Kitab al-Kafi Man Lā Yahduruhu al-Faqih Tahdhib al-Ahkām Al-Istibsār