Clean and unclean means in the bible: It had great influence on their entire religious and social lives. This was first applied to food. Some animals, birds and fish were considered clean enough to be eaten. Others were not and could not be. Lev. 11; Deut. 14:3-20. It was forbidden to eat flesh from any wild animal or die by itself. 22:31; Lev. 17:15; 22:8; Deut. 14:21. Blood, considered to contain the life, was forbidden for Israelites. It had to be removed and covered Gen. 9; 4; Lev. 17:10-14; 19:26; Deut. 12:16, 23-25; 15:23. Fat was also forbidden. It belonged to God Lev. 7:22-27.
(in Bible Dictionary)