What is the "tyranny of the majority" and what part of the constitution protects us from it?

The concept of the tyranny of the majority is that a larger group of people may vote to reduce the rights of the smaller group of people. An example would be the Jim Crow laws of the Southern states prior to the Civil Rights Movement. 

The Constitution, especially the Equal Protection clause, protects us from this. The US was founded on the idea that, "All men are created equal," thus we all have equal rights