Pigs are omnivores — they eat both plants and meat — and on small farms, they're fed kitchen leftovers as well as their basic diet. Their dining habits have given pigs the reputation of being greedy, and led to the informal use of pig to mean "greedy person," and pig out to mean "eat voraciously." Another colloquial meaning of pig, one that's been considered derogatory since it was coined in the nineteenth century, is "police officer."