The Silent generation is People born before 1946 were called.
The Baby Boomers, are people born between 1946 and 1959.
Generation X, are the people who have been born between 1960 and 1979.
And Generation Y, are the people born between 1980 and 2009.
In Hong Kong we also call "八十後", meaning "after 80"
Why do we call the last group Generation Y?
A Cartonist has a perfect illustration: