The food chain starting from plants and moving upwards to herbivores followed by carnivores is said to be made up of different trophic levels. The efficiency with which energy can move from one trophic level to the one above it is called ecological efficiency. Or in other words it is efficiency with which organisms in a trophic level take energy from a level below them and convert it to a form that can be passed on to organisms at a higher trophic level.
Plants and fungi which have the ability to carry out photosynthesis are the organisms at the lowest level of the food chain. When plants are consumed by herbivores around half of the energy that was absorbed by the plants is ingested by them. After the use of energy in bodily process by herbivores around 1/8 - 1/10 of the energy from the plants can be passed on to carnivores.
The transfer of energy to levels higher up in the food chain is highly inefficient in nature. This is one of the reasons why it is easier for humans to produce food to feed themselves if they adopt a vegetarian diet than a non-vegetarian one.