In a more general sense, animals are loosely considered carnivores if their feeding behaviour consists of preying on other animals rather than grazing on plants. Animals that must eat meat in order to thrive are referred to as obligate carnivore]]s.

Plants that capture and digest insects are called carnivorous plants. Similarly fungi that capture microscopic animals are often called carnivorous fungi.

The designation "hypercarnivore" is used to describe animals that exclusively feed on animal tissue. Additionally, this term is also used in [[paleobiology to describe taxa of animals which have an increased slicing component of their dentition relative to the grinding component.

Classification

Carnivores that eat insects and similar invertebrates primarily or exclusively are called insectivores, while those that eat fish primarily or exclusively are called piscivores. Carnivory that entails the consumption of members of an organism's own species is referred to as cannibalism. This includes sexual cannibalism and cannibalistic infanticide.

The word "carnivore" sometimes refers to the mammalian Order Carnivora, but this is misleading. Although many Carnivora fit the first definition of being exclusively meat eaters, not all do. For example, bears are members of Carnivora that are not carnivores in the dietary sense, and pandas are almost exclusively herbivorous. Likewise, some full-time (dolphins, shrews) and part-time (humans, pigs) meat-eating species among mammals, let alone all carnivorous non-mammals, are not members of Carnivora.

Outside of the animal kingdom, there are several genera containing carnivorous plants and several phyla containing carnivorous fungi. The former are predominantly insectivores, while the latter prey mostly on microscopic invertebrates such as nematodes, amoeba and springtails.

Prehistoric mammals of the crown-clade Carnivoramorpha (Carnivora and Miacoidea without Creodonta), along with the early Order Creodonta, and some mammals of the even early Order Cimolesta, were true carnivores. The earliest carnivorous mammal is considered to be the Cimolestes that existed during the Late Cretaceous and Tertiary Periods in North America about 65 million years ago. Most species of Cimolestes were mouse to rat-sized, but the Late Cretaceous Cimolestes magnus reached the size of a marmot, making it one of the largest Mesozoic mammals known (20-60g). The cheek teeth combined the functions of piercing, shearing and grinding, and the molars of Palaeoryctes had extremely high and acute cusps that had little function other than piercing. The dentition of Cimolestes foreshadows the same cutting structures seen in all later carnivores. While the earlier smaller species were insectivores, the later marmot-sized Cimolestes magnus probably took larger prey and were definitely a carnivore to some degree. The cheek teeth of Hyracolestes ermineus (an ermine-like shrew - 40g) and Sarcodon pygmaeus ("pygmy flesh tooth" - 75g), were common in the Latest Paleocene of Mongolia and China and occupied the small predator niche. The cheek teeth show the same characteristic notches that serve in today's carnivores to hold flesh in place to shear apart with cutting ridges. The theropod dinosaurs such as Tyrannosaurus rex that existed during the late Cretaceous, although not mammals, were "obligate carnivores".