Definitions
Half these arguments are about the word.
A surprising number of debates go nowhere because the two people are using different definitions. This is the one this site works from.
The definition we use
The Vegan Society, whose founders coined the word in 1944, defines veganism as a philosophy and way of living that seeks to exclude all forms of exploitation of and cruelty to animals, for food, clothing or any other purpose, so far as that is possible and practicable.
A philosophy and way of living which seeks to exclude all forms of exploitation of, and cruelty to, animals.
Three things follow from that wording, and all three get missed.
It is a philosophy, not a diet. Food is the largest part of it in practice, but the definition is about not treating animals as resources, which reaches clothing, entertainment and testing as well.
It covers exploitation, not only cruelty. A practice does not have to involve suffering to be excluded. An animal killed painlessly after a comfortable life has still been used as a means to an end, and that is the thing being objected to.
And it is a direction, not a purity test. Nobody participates in a modern economy without some animal use somewhere in the supply chain. The definition accepts that and asks what is avoidable.
What possible and practicable actually means
This is the part that gets stretched, usually by people arguing in good faith, so it is worth being exact. The qualifier is about circumstance, not preference.
It covers someone with a medical condition that limits their options, someone in a food desert with no alternative on the shelf, someone whose survival depends on what is available rather than what they would choose, and a child who does not control what they are fed.
It does not cover finding the alternative less convenient, less familiar or less enjoyable. Those are preferences, not constraints, and the definition is not built to accommodate them.
Those are real feelings, and they explain a great deal of behaviour, including most of ours before we changed. The distinction matters because almost every argument on this site turns out, somewhere, to be an attempt to move a preference into the constraint column.
The variations, and what each one leaves out
Plant-based, or dietary vegan
Describes what someone eats and nothing else. Often chosen for health or environmental reasons, and entirely compatible with buying leather or visiting a zoo. Useful as a description of a diet. It is not a position on how animals may be treated, and it is not what this site means by vegan.
Ethical veganism
The full definition above, held as a moral commitment. In the UK this is a legally recognised position: in Casamitjana v League Against Cruel Sports (2020), an employment tribunal held that ethical veganism is a philosophical belief protected under the Equality Act 2010. This is the sense used throughout the site.
Abolitionist and welfarist
A disagreement about strategy rather than about the definition. Abolitionists hold that animals should not be used at all, and that campaigning for better conditions makes the use more comfortable to continue. Welfarists hold that reducing suffering now is worth doing on its own terms. The definition we use does not settle this, and the site does not need to: both sides agree that a preference for the taste does not justify the harm.
Reducetarian and flexitarian
Eating less animal product without excluding it. Worth taking seriously, because less harm is less harm and most vegans arrived by something like this route. But it is a rate of consumption, not a position on whether the consumption is justified, so it cannot answer the arguments on this site. It can only reduce how often they come up.
Vegetarianism
Excludes meat but permits dairy and eggs, which are the industries behind some of the harms people find hardest to defend once they look at them: the separation of calves from mothers, and the killing of male chicks and of hens past laying age.
Why this one
Because it is the oldest and most widely recognised definition, because it is about animals rather than about the person following it, and because it is specific enough to argue with. A definition you cannot be wrong about is not much use in a debate.
It also sets the standard the responses on this site are held to. If an argument succeeds against this definition, we have to say so.