Thank you for your question on Elite Theory.
The definition of elite theory is a theory related to the state, which serves to explain how man can never be alleviated of his place in a elitist, hierarchical society. It is a reaction, in fact a rejection of the Marxian notion, which believes that an egalitarian state could be achieved post class struggle.
The theory is geared around the idea that there are a small minority who are in control of society, independent of the elected government. This is not something that can be overridden or abated. This small minority are said to hold the greatest power and can strongly influence decision making in the upper echelons of society, including the decisions that help shape and run society.
Elite Theory also negates the concept of pluralism, in perceiving true democracy as an impracticable ideal.
Hopefully this answers your question.