The source of all food is the activity of autotrophs, mainly photosynthesis by plants.
They are called producers because only they can manufacture food from inorganic raw materials.
This food feeds herbivores, called primary consumers.
Carnivores that feed on herbivores are called secondary consumers.
Carnivores that feed on other carnivores are tertiary (or higher) consumers.
Such a path of food consumption is called a food chain.
Each level of consumption in a food chain is called a trophic level.
The table gives one example of a food chain and the trophic levels represented in it.