Vegetarianism has its origins in 3200 BC, when ancient Egyptian civilizations started adopting vegetarian diets based on the belief that abstaining from meat consumption would facilitate reincarnation. In India, another important cradle of vegetarianism, this practice was also associated with the fact that Hindus see cows as sacred and uphold nonviolence principles.

Later, Greek philosophers also adopted a vegetarian diet, with Pythagoras being a leading figure among them—indeed, for many centuries, vegetarianism was known as the “Pythagorean” diet.
In the Christian Era, vegetarianism lost its strength, gaining some visibility again only in the late 18th and early 19th centuries, when Darwin’s theory of evolution challenged the Church’s views that animals had no souls, and that their only purpose on Earth was to serve human beings.
 
Throughout history, the expansion of vegetarianism has been associated with religions that preach respect for all living beings and adopt nonviolence principles, such as Hinduism, Jainism, Sikhism, Buddhism, the Hare Krishna movement, Rastafarian movement and the Seventh-day Adventist Church.

In addition, in the 20th and 21st centuries, science has observed several health benefits potentially associated with the reduction in meat consumption.
Such benefits have strengthened the practice of vegetarianism around the world, and attracted more and more followers.
 
The current worldwide prevalence of vegetarianism indicate that Asia is the continent with the highest prevalence, with 19 percent of the population adopting this practice.
India tops all world countries with almost 40% of its population living this life.
The prevalence in Africa and the Middle East is about 16 percent; and in Central and South America, 8 percent.
And the lowest prevalence of vegetarianism is found in North America (about 6 percent of the population are vegetarians) and Europe, where vegetarianism is adopted by only 5 percent of the population.
 
Vegetarianism encompasses different types of diets, classified according to how restrictive they are.
Generally, vegetarianism is understood as the exclusion of meat from one’s diet, but other less restrictive eating patterns can also be classified within the scope of vegetarianism.
These types include;
Flexitarians, who consume meat sporadically, or even once a week.
Pescatarians, who avoid all meat, except fish and seafood.
Ovolactovegetarians, who banish all types of meat but consume products of animal origin,
such as eggs and dairy products.
Ovovegetarians, who avoids all meat but consume eggs and plant based food.
Lactovegetarians, those who include dairy products such as milk etc.. in their diet together with the usual plant based diet.
Vegans, follow strict vegetarian diet, which excludes all foods of animal origin.

Veganism is a broader concept, which involves the adoption of a strict vegetarian diet, as well as the exclusion of other consumer items made from animal products, or which rely on animal exploitation, such as cosmetics and clothing items.

"A strict vegetarian diet is often referred to as a vegan diet."

Different motivations can lead to adopting a vegetarian diet.
Ethical concerns are the main reasons, building on the idea that animal slaughter for human consumption is morally inappropriate.
Another important motivation is health and the potential beneficial effects of vegetarianism.
Religions that encourage abstaining from meat consumption and concerns about the environmental impacts of meat production are also important motivators for adopting vegetarianism.

Reference;

1. International Journal of Environmental Research and Public Health, Pub.April 12, 2021.
2. BetterHealth Channel, Vegetarian and vegan eating