An obligate
carnivore is an animal which must eat
meat to survive. These animals lack the ability to digest other types of food and will die or become
malnourished without meet.
Cats are
obligate carnivores, as are other animals in the cat family.
Dogs are not - although their ancestors mainly ate meat in the wild, they don't have to in captivity - lots of dog food is made of rice and other fillers.
Humans are not obligate
carnivores - although they did evolve eating meat, they don't have to eat animal products to survive (although if they do not they need to eat
protein in other forms, like that nasty goo known as
tofu.
This concept was not grasped by a legendary idiot from the Bay Area who once tried to force his cat to go Vegan. The cat nearly died. Regardless of human morals, cats must eat meat, or they will die.