A predator hunts for prey which is the organism it attacks. This is usually in reference to one animal consuming another animal, for example, an eagle consuming a fish. In predation, the predator is a secondary consumer eating the primary consumer. Or, it can be a third-level consumer, eating the secondary consumer. Herbivores are organisms that eat autotrophs, or plant-based foods. Herbivory is a type of consumption just as a predator consumes a prey, however, in herbivory, those consumers are deemed primary consumers. They are not killing another animal, rather, they are consuming a plant which is at the bottom of the food chain.
Herbivores can be considered predators as predators are noted as organisms that directly kill an organism. Just as some pigs eat the roots of plants or how any other organism can eat a plant so that it is fully uprooted and dies. However, it can also be considered a parasite as some insects or larvae of insects only eat parts of the plant which regenerates through the tolerance of the plant. In this way they are draining the resources of the plant but not directly killing it
A Herbivore is an animal which consumes only plants while a Carnivore consumes on meat and an Omnivore sits in the middle - cable of consuming either.
A predator is an animal which preys for it's prey for the need for its survival. A prey is an animal that is consumed by a predator.
To be able to be called a predator, an animal has to be able to eat the flesh/meat of another animal - i.e the animal can only be called a carnivore or an omnivore.
Herbivores cannot be called predators since they do not prey for food since their bodies aren't designed to be able to digest meat. Herbivores are generally the ones that become the prey for the predators.
Example: A tiger is a carnivore and a predator while a deer is a herbivore and a prey - not a predator