Primarily, a living creature who consumes meat - i.e.: poultry, pork, beef, fish. Many human meat-eaters are disrespectful towards those who don't eat meat, particularly towards vegans, often writing bad definitions of them in urban dictionary. Such people are often bad at spelling and consistently illogical in their responses to vegetarians and vegans.
Omnivore: 'I could murder a nice, juicy steak. Do you want one?'
Vegan: 'No thankyou, I'm a vegan.'
Omnivore: 'Oh, one of those. I suppose you're going to lecture me on how bad it is to eat meat.' (waves meat in vegan's face).
Vegan: (looks at omnivore disdainfully) No, but I would prefer it if you didn't wave meat in my face. (Waves tofu burger in omnivore's face).
Omnivore: (Shrinks back in true terror).