Popular definition: "rule by the people." "rule (kratos) by the people (demos)."
The Procedural Definition (Joseph Schumpeter): "that institutional arrangement for arriving at political decisions in which individuals acquire the power to decide by means of a competitive struggle for the people's vote."
The Elite Accountability Definition: "a system of governance in which rulers are held accountable for their actions in the public realm by citizens, acting indirectly through the competition and cooperation of their elected representatives."
The Rights Addendum: Democracy cannot be guaranteed without the creation and defense (by states) of civil and political rights (others add "social," "economic," and human rights).