I looked this up, since I've always been curious about it, too. This is what I found...
Generation X
SYLLABICATION: Gen·er·a·tion X
PRONUNCIATION: AUDIO: jn-rshn KEY
NOUN: The generation following the postWorld War II baby boom, especially people born in the United States and Canada from the early
1960s to the late 1970s.
ETYMOLOGY: After Generation X, a novel by Douglas Coupland (born 1961), Canadian writer.
OTHER FORMS: Generation Xer (eksr) NOUN
Generation Y
NOUN: The generation following Generation X, especially people born in the United States and Canada from the early 1980s to the late 1990s.
Now I know! I guess my grandchildren (should I have them) will be generation z...but what after that????
