Unchecked refers to something that is not limited, controlled, or supervised. In relation to government authority, it means there are no checks and balances in place to prevent abuse or misuse of power.
Related terms
Separation of Powers: The division of governmental powers among different branches (such as executive, legislative, and judicial) in order to prevent any one branch from becoming too powerful.
Judicial Review: The power of courts to determine whether laws and actions taken by the other branches of government are constitutional.
Accountability: Being responsible for one's actions and being answerable for them; often involves mechanisms for oversight and transparency.