Typically, a secondary consumer is a small animal that eats another animal and by this definition, an owl is a secondary consumer. However, an owl can technically be considered a secondary consumer or a tertiary consumer, depending on what it is eating at the time.
In a food web or chain, each organism has its place and function. The producers are plants which produce food for primary consumers. Secondary consumers eat the primary consumers and tertiary consumers are animals such as snakes, lions and foxes that eat secondary consumers.
Besides being broken down in this way, the animal kingdom can also be classified into other groups. For example, herbivores eat plant matter and nothing else. Carnivores only eat meat and omnivores, like humans, eat both plants and animals.