Used in the United States Declaration of Independence to mean "no man is born inherently better or worse than any of the others." The corollary, then, is that all men have the same unalienable rights to "life, liberty, and the pursuit of happiness."
An important principle, because at the time it was written it wasn't seriously applied to include women, slaves, or poor people. The fact that Americans have since come to conclude the opposite is a testimony to its validity.