Groupings such as baby boomer and millennial appeal to those seeking to measure social and cultural change, but the cutoffs are fuzzy, and critics say the descriptions can be insulting stereotypes.

Baby boomers. Generation X. Millennials.

These are the familiar sobriquets of recent generations, but what exactly defines the cohorts, and what, if anything, do their labels reveal?

A generation, in this sense, refers to people associated with a distinct era of history based on their years of birth. But the cutoffs are fuzzy, and critics charge that the descriptions are little more than insulting stereotypes: Boomers, we’re told, are ambitious workaholics. Gen Xers are disenfranchised cynics. Millennials are self-entitled narcissists.

More: Analysis of the Generations Isn’t an Exact Science