Ecological efficiency is the amount of energy that is transferred from one trophic level to the
next. It is defined as the energy supply available to trophic level N + 1, divided by the energy consumed by trophic level N. This follows the 10% rule, which states that roughly 10% of the energy at one level will be available to be used by the next level. Hence if ecosystem A has higher ecological efficiency than B, then it means energy transfer between trophic levels is more efficient in ecosystem A than B.
For example, in an ecological pyramid, producers are consumed by primary consumers. The consumers eat these producers, but only about 10% of what they consume actually becomes new biomass for the primary consumer. So if a wolf eats a deer, only 10% of what was consumed becomes new wolf biomass.