In Germany, a vegan is someone who doesn’t consume any animal products, this includes (apart from meat, egg and dairy) honey, silk and leather. But vegans can eat all plant products. German vegans don’t refrain from animal products because of religious reasons but because they oppose animal cruelty.

I agree with Miriam's definition, although I'd add that not all vegans are primarily concerned with animal cruelty. Most of them are, but some people are vegan for environmental reasons (because a lot of the industries that produce meat and animal products do significant damage to the environment in the process, apart from the direct harm they do to the animals), and some people are vegan for health reasons (for example, being vegan has been shown to reduce the severity and frequency of episodes in people with Multiple Sclerosis).

I know there are also some vegans who also boycott plant products that are produced, harvested, or processed in ways that harm animals. This can include harming insects, for instance by using pesticides. It's hard to imagine any plant that can really be grown and harvested without harming any insects, but I don't know... maybe there's some connection there with garlic and onions?

I can infer that your student must have been Indian. As an Indian she would be aware of the onion garlic thing even if she isn't Hindu herself.

The Quora answer which Miriam referred to is only partially correct. First, the root vegetable idea isn't Buddhist but that of another offshoot sect of Hinduism called Jains. There are two kinds of Jains and only one of those go by that rule. Buddhists eat pretty much everything, there are no explicit dietary restrictions in Buddhism. You only need to look at the cuisine of Buddhist majority countries such as Thailand, Laos and Myanmar as well as China at one time to realize that.

Technically there are no dietary restrictions in Hinduism either in any of the recognized scriptures. There is nothing similar to the kashrut laws of the Jews or the halal rules of Islam. But even so there are certain social customs which appear to have taken on religious overtones in time.

The actual idea is a bit more complex, which I will try to reduce to the bare essence here. There are three lifestyles: the spiritual, the royal and the consumerist one. The first is about simple living, the second about wealth and power, and the third about indulgence. Under the spiritual way, things like onion and garlic are considered to cause body heat, desire and restlessness. So are things like fish, meat and eggs, but it does not include dairy and honey like present day vegans do.

It's for that reason onion and garlic are not used during spiritual pursuit or payer rituals. This has a weird outcome: you'll find plenty of otherwise non vegetarian people who will abstain from all those things including onion and garlic for a day, several days or even a full month when those are considered auspicious and ideal for prayer and worship.

On Quora there’s a thread about why garlic and onion aren’t considered vegetarian by some religious groups: <a href="https://www.quora.com/Why-are-onions-and-garlic-not-vegetarian" target="_blank">https://www.quora.com/Why-are-onions-and-garlic-not-vegetarian</a>;

I think like Miriam. I've been vegeterian for more or less 12 years, and the basic is food, not eating meat or fish, but I've eaten eggs, honey, milk, cheese... And I tried to avoid animal products like leather, products tested with animals etc.

I know some vegans and they don't eat animal products (not milk, honey, bee pollen...) and they avoid animal products too.