One way to define it, another is how deaths occur. I would think that slaughtering an animal in an abattoir is possibly more humane than a rodent, rabbit, possum etc being mamed by agricultural equipment or subject to poisons, which could result in a slow painful death.
From the work Matthew Evans has done and assuming his analysis is correct, he indicates that 25x more animals die for each unit of plant protein compared to animal protein. I suspect that the plant protein number is weighted by ‘lower order’ animals such as amphibians, reptiles, insects, arachnids etc.
It is interesting to note that hard core vegans won’t eat honey due to it being produced by an animal which is used for making a food…and this does suggest that they value lower order animals equally to higher order animals.
I suspect that many vegans also chose organic food potentially thinking that impacts on animals are less, but organic foods does not mean animal safe…just synethic chemical free. Organic farmers also use practices which impact on animals resulting in their death or maming.
What Matthew Evans is quite interesting and does provide food for thought. It also questions values and ethics of those who more recently are trying to change the values of others (vegan farm trespass and protests).