If someone practises vegetarianism, they never eat meat or fish.
Vegetarianism is on the increase in Britain.
vegetarianism in British English
(ˌvɛdʒɪˈtɛərɪəˌnɪzəm)
noun
the principle or practice of excluding all meat and fish, and sometimes, in the case of vegans, all animal products (such as eggs, cheese, etc) from one's diet