Consent of the governed
The phrase is often attributed to John Locke, but the idea was around much earlier. The concept of consent of the governed appears in the Scottish Declaration of Arbroath (1320) which states that Lord Robert, because of "Divine Providence" along with "the due consent and assent of us all, have made him our prince and king."
The United States was the first nation of modern times to break away from the colonial rule of a distant monarch by invoking "consent of the governed" as a right in the United States Declaration of Independence.
Today, consent of the governed is a presumptive aspect of all democracies. Indeed, any government that cannot plausibly claim to rule by consent of the governed tends not to enjoy the benefit of the doubt about their legitimacy, either by their own people or the peoples of other nations.
A general criterion for consent of the governed is that it is obtained through the practice of regular elections that feature broad (if not universal) suffrage (i.e., rights to vote).
This concept of consent through free and regular elections was earlier expressed in the Virginia Declaration of Rights, written by George Mason in 1776 (see excerpt below):
"Section 6. That elections of members to serve as representatives of the people, in assembly ought to be free; and that all men, having sufficient evidence of permanent common interest with, and attachment to, the community, have the right of suffrage and cannot be taxed or deprived of their property for public uses without their own consent or that of their representatives so elected, nor bound by any law to which they have not, in like manner, assented for the public good".
That some choose not to vote would not prevent the People as a whole, via majority rule, from establishing their consent via elections, just as the existence of Representatives elected by the People does not mean the laws approved by the Representatives are invalid. Under this approach, the government must come before the People for continuing authority at each election and establish through open and transparent checks and balances that it has achieved a mandate to exercise authority in a fair and incontestable manner.
See also Washington DC (voting rights and representation).