Rule of Law generally means that all citizens, regardless of station, are held to account to the standards set forth in law. In other words, nobody is "above the law". Use this tag to discuss the concept, as well as political instances where it is abused.
Generally speaking, Rule of Law means that all citizens (even those in political power) are held to account to the standards set forth by the law. The antithesis of this would be a dictatorship or oligarchy, where a ruler or ruling class is "above the law", meaning they need not fear any enforcement.
The World Justice Project has a decent breakdown of the key concepts necessary for Rule of Law
Accountability - The government as well as private actors are accountable under the law.
Just Laws - The laws are clear, publicized, stable, and just; are applied evenly; and protect fundamental rights, including the security of persons and property and certain core human rights.
Open Government - The processes by which the laws are enacted, administered, and enforced are accessible, fair, and efficient.
Accessible & Impartial Dispute Resolution - Justice is delivered timely by competent, ethical, and independent representatives and neutrals who are accessible, have adequate resources, and reflect the makeup of the communities they serve.