Ceremonial Cleanness is described at length in the Bible as the state in which a person may enter into the presence of the Lord. Scripture says, about the Heavenly city:
27 There will in no way enter into it anything profane, or one who causes an abomination or a lie, but only those who are written in the Lamb’s book of life. Revelation 21:27WEB
There is a difference between the Sinai Covenant and New Covenant when it comes to the definition of cleanness:
15 A voice came to him again the second time, “What God has cleansed, you must not call unclean.” Acts 10:15WEB
Several behaviors could cause a person to become unclean, and in general a clean thing could be made unclean by coming into contact with an unclean thing. The notable exception to this belongs to Jesus, who touches unclean people and makes them clean, and who is restoring the world to a state of ceremonial cleanness. This topic will overlap with a wide variety of other topics, as there are many actions which can make someone unclean: some criminal, some sinful, and some mundane.