Extract usually obtained from a newly-born calf stomach. Rennet contains the enzymes rennin and a little amount of pepsin. The older the veal calf, the more pepsin will be found in the rennet. Rennet can also be derived from synthetic sources or from bacteria and fungus
Rennet is often used in making cheese and is listed under the ingredients as enzymes rather than rennet.
Please check with your cheese manufacturers to make sure they are using vegetarian friendly rennet. Also, please remember to look into this when eating pizza. Just because you think you`re eating a vegetarian pizza, doesn`t mean the cheese is vegetarian or the dough doesn`t contain eggs.