The phrase tyranny of the majority, used in discussing systems of democracy and majority rule, is a criticism of the scenario in which decisions made by a majority under that system would place that majority's interests so far above a minority's interest as to be comparable in cruelty to "tyrannical" despots.
Limits on the decisions that can be made by such majorities, such as constitutional limits on the powers of parliament and use of a bill of rights in a parliamentary democracy, are commonly meant to avoid the problem.
The phrase has variously been sourced to John Stuart Mill in On Liberty (1859).
https://en.wikipedia.org/wiki/Tyranny_of_the_majority
Mill's work could be considered a reaction to this social control by the majority and his advocacy of individual decision-making over the self. The famous 'Harm Principle' is also articulated in this work: people can do anything they like as long as it does not harm others.
All branches of liberalism—as well as other political ideologies—consider this to be one of their core principles. However, they often disagree on what exactly constitutes harm.
https://en.wikipedia.org/wiki/On_Liberty
