The term "millennials" was coined before "Generation Y," and the initial definition was children born during or after 1982, which is more or less where it stands now (I've seen the definition of millennials get extended back to 1980, but rarely if ever into the 70's.) Generation X is actually the one that absorbed the originally defined Generation Y, which comprised children born from 1974-1980.

Citation: https://en.wikipedia.org/wiki/Millennials#Terminology_and_et...