noun: A person who was born during the cusp years between any two of the named generational divisions of the 20th and 21st centuries.
The categorization of generations is highly generalized, arbitrary, and unscientific with a pretty wide span of years encompassing each generation. In spite of this, generations and their corresponding characteristics are discussed quite frequently in the news and media. This is probably because we as humans enjoy categorizing and looking for patterns in just about everything including our supposed shared experience, behavior, and nostalgia with people somewhat near to us in age.
At any rate, the years of transition between each generation are vague, and people born in that little window might find that they embody characteristics of both generations they walk the line between. Cuspers don't fit so neatly into the facts and figures of the generations that the news is so fond of citing.
Examples of cuspers include:
Silent Generation/Baby Boomers: People born in the early to mid 1940s
Baby Boomers/Generation X: People born in the early to mid 1960s
Generation X/Millennials: People born in the late 1970s to early 1980s (also dubbed "The Oregon Trail Generation.")
Millennials/iGeneration: People born in the late 1990s to early 2000s
I was born in 1981, making me a Generation X/Millennial cusper. I have significent memory of an analog world and came of age with AOL and early internet. I have a sister born in 1973, putting her squarely in Generation X, and a brother born in 1992, making him such a Millennial. :-)
As silly as all of this is, I admit I get a little pleasure out of generational categorization. And popular culture and media make it nearly impossible to ignore.