In Islamic law, najis (Arabic: نجس) means ritually unclean.
Ritual purification is then required before religious duties such as regular prayers are performed.
According to the Shafi'i school of Sunni Islamic jurisprudence, as systematised by Al-Nawawi in his book Minhadj, the following things are najis: wine and other spirituous drinks, dogs, swine, blood, excrements, and the milk of animals whose meat is forbidden by Islam.
[2] To the list of impure things enumerated by al-Nawawi, Shi’a jurists traditionally add dead bodies and non-believers.
[1][3] Additionally, meat of any animal which is killed in a manner other than that prescribed by Islam is najis.